Color image forming method and color image forming apparatus

ABSTRACT

A color image forming method, including: forming electrostatic latent image on electrostatic latent image bearing member; developing the image to form visible image with at least two toners containing releasing agent and selected from black, magenta, cyan and yellow toners; transferring the visible image to recording medium; fixing the transferred image thereon with fixing member having no releasing agent on surface thereof; and forming overcoat layer on the fixed image by polymerizing overcoat composition, wherein when lightness—L 1 , chromaticity—a 1  and chromaticity—b 1  according to L*a*b* color system of the fixed image formed with the at least two toners and lightness—L 2 , chromaticity—a 2  and chromaticity-b 2  of the fixed image after the overcoat composition is dropped at 0.4 mg/cm 2  from height of 10 mm above the fixed image and the overcoat composition is removed after 10 seconds have passed are applied to the following formula (1), color difference ΔE* is 3.0 to 30.0:
 
Δ E *=[( a 2− a 1) 2 +( b 2− b 1) 2 +( L 2− L 1) 2 ] 1/2   (1).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a color image forming method and acolor image forming apparatus.

2. Description of the Related Art

For the purpose of imparting a high-grade sense to an image andincreasing the durability thereof, an overcoat layer of varnish or thelike has been conventionally provided on the surface of the image thatappears on color pages, etc., of tickets, catalogues and magazines.Particularly, in commercial fields, varnish layers are formed on imagesprinted in a great number by screen printing, etc. Although these imagesare in general high in percentage of image area, they can be prepared asbeautiful images having a high-grade sense due to good compatibility ofvarnish with ink used in screen printing.

However, in recent years, there has been found an increasing demand forfrequently changing and updating information to be printed. Therefore, aprinting method such as screen printing which prepares an original textfor printing is not economically feasible in many cases and so-calledprint on-demand has started to be used.

A recording method used in the above-described print on-demand usuallyincludes an electrophotographic method and an inkjet method. The inkjetmethod is suitable for a small quantity of printed matter but unable tocope with a case that images are formed quickly and in a great quantitydue to the long drying time of ink. Further, ink which has permeatedinto a recording medium such as paper will cause expansion orcontraction of the paper to result in a slight change in thickness ofthe paper depending on a site of an image. It is, therefore, difficultto stack in an orderly manner a large quantity of ink recorded matter onwhich images are formed. As a result, the electrophotographic methodusing toner currently prevails. In the electrophotographic method, imageinformation is exposed on a charged photoconductor to form a latentimage, toner is used to develop the latent image, the thus obtainedtoner image is transferred to a recording medium such as paper and,thereafter, the transferred image is thermally fixed on the paper.

As a technology on the overcoat layer used in the electrophotographicmethod, there has been proposed, for example, an overcoat compositionwhich is based on water, free of ammonia and low in static surfacetension as an overcoat composition used for a to-be-printed matter onwhich fixing oil is coated (refer to Japanese Patent ApplicationLaid-Open (JP-A) No. 2007-277547).

There have been also proposed a resin forming device which forms asilicone resin layer on a printing surface to protect the printingsurface, giving waterproofing and imparting gloss, and an image formingapparatus which is provided with the resin forming device (refer toJapanese Patent Application Laid-Open (JP-A) No. 10-309876).

Further, there has been proposed a method for printing metal containersin which an electrophotographic method is used to efficiently printvarious types of printed matter in a small lot and a finish varnishlayer is provided to protect a toner layer and impart gloss (refer toJapanese Patent (JP-B) No. 2522333).

The methods proposed above are all preferable in providing an overcoatlayer on an electrophotographically formed image.

For an improvement in mold releasability, silicone oil has been coatedin a great quantity on the surface of a fixing roller of a fixing unitused in an electrophotographic method. However, toner is greatlydifferent in mold releasability between a site which has silicone oil onthe fixing roller and a site which is free of silicone oil. Therefore, asite on which silicone oil is not coated will cause streaks which aredifferent in gloss. Large-scale printing could increase costsaccordingly, if the printing should fail. Further, where silicone oiladheres on a floor, the floor becomes quite slippery. Still further,since complete removal of silicone oil is difficult, full attention isrequired in supplementing the silicone oil and maintaining the fixingunit. And, this is troublesome for those involved in maintenance work.

In recent years, so-called oilless fixing has been carried out in whichwax-containing toner is used to heat a toner image on fixing, allowingthe wax contained in the toner to ooze out on the surface of the image,thereby securing mold releasability of the image from a fixing roller.In the oilless fixing, where wax is present in a greater quantitybetween the image on fixing and the fixing roller, the moldreleasability of the image from the fixing roller is further improved.For this reason, wax is added to toner to the extent possible, and suchwax that easily melts at a low temperature is used to appropriatelyadjust fixing conditions (pressure of the fixing roller, fixingtemperature and fixing time) which facilitates melting of the wax.

However, in an attempt to provide an overcoat layer on an image on whichthe above-described oilless fixing has been carried out, wax on a fixedimage repels an overcoat composition. Thus, there are problems that theovercoat layer becomes quite thin in thickness at a site great in imagearea, the cured overcoat layer is not firmly attached on an oillessfixed image and scratching or bending of the surface results indetachment of the overcoat layer.

Further, a color image is formed by overlapping respective yellow,magenta, cyan and black color toners on a recording medium. Therefore,the color image is greater in quantity of toner adhered than asingle-color black-and-white image and also greater in content of wax.As a result, the color image is further decreased in attachment propertyof the overcoat layer than the black-and-white image, which makes theabove problems more apparent.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a color image formingmethod by which it is possible to form a high-grade and beautiful imagegreat in durability even in formation of a color image that is greaterin content of a releasing agent than a black-and-white image and alsolower in attachment property to an overcoat layer.

A color image forming method of the present invention for solving theabove-described problems includes: an electrostatic latent image formingstep which forms an electrostatic latent image on an electrostaticlatent image bearing member; a development step which develops theelectrostatic latent image to form a visible image with at least twotoners each containing a releasing agent and being selected from blacktoner, magenta toner, cyan toner and yellow toner; a transfer step whichtransfers the visible image to a recording medium; a fixing step whichfixes a transferred image on the recording medium with a fixing memberhaving no releasing agent on a surface thereof, and an overcoat layerforming step which forms an overcoat layer on the fixed image bypolymerizing an overcoat composition, wherein when lightness L1,chromaticity a1 and chromaticity b1 according to an L*a*b* color systemof the fixed image formed with the at least two toners as well aslightness L2, chromaticity a2 and chromaticity b2 according to theL*a*b* color system of the fixed image obtained after the overcoatcomposition is dropped at 0.4 mg/cm² from a height of 10 mm above thefixed image and the overcoat composition is removed after 10 secondshave passed are applied to the following formula (1), a color differenceΔE* is from 3.0 to 30.0:ΔE*=[(a2−a1)²+(b2−b1)²+(L2−L1)²]^(1/2)  (1).

According to the present invention, it is possible to provide a colorimage forming method which is capable of solving the above-describedvarious conventional problems, attaining the above object and alsoforming a high-grade beautiful image great in durability even information of a color image greater in content of a releasing agent thana black-and-white image and lower in attachment property to an overcoatlayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a reflection electron image of an oilless fixed image whichis poorly bonded with a chemically modified overcoat layer.

FIG. 1B is a binarization image of the image given in FIG. 1A.

FIG. 2A is a reflection electron image of an oilless fixed image whichis favorably bonded with a chemically modified overcoat layer.

FIG. 2B is a binarization image of the image given in FIG. 2A.

FIG. 3 is a schematic diagram which shows one example of an overcoatlayer forming unit.

FIG. 4 is a schematic diagram which shows one example of a color imageforming apparatus of the present invention.

FIG. 5 is a schematic diagram which shows another example of the colorimage forming apparatus of the present invention.

FIG. 6 is an enlarged view which shows a tandem-type developing devicegiven in FIG. 5.

FIG. 7 is a schematic diagram which shows a device used in a fusionproperty test.

DETAILED DESCRIPTION OF THE INVENTION

(Color Image Forming Method and Color Image Forming Apparatus)

A color image forming method of the present invention includes anelectrostatic latent image forming step, a development step, a transferstep, a fixing step, and an overcoat layer forming step and furtherincludes other steps, whenever necessary.

A color image forming apparatus of the present invention includes anelectrostatic latent image bearing member, an electrostatic latent imageforming unit, a development unit, a transfer unit, a fixing unit, and anovercoat layer forming unit and further includes other units, whenevernecessary.

The color image forming method of the present invention can be carriedout favorably by the color image forming apparatus of the presentinvention, the electrostatic latent image forming step can be carriedout by the electrostatic latent image forming unit, the development stepcan be carried out by the development unit, the transfer step can becarried out by the transfer unit, the fixing step can be carried out bythe fixing unit, the overcoat layer forming step can be carried out bythe overcoat layer forming unit, and the other steps can be carried outby the other units.

An overcoat layer formed by being cured by light or electron beamradiation on an oilless fixed image which has been subjected to oillessfixing is in general favorably attached to toner starting particleswhich contain a binding resin such as polyester and polystyrene.However, since the oilless fixed image contains a releasing agent (wax),the toner starting particles are required to be attached more firmly tothe overcoat layer. The toner starting particles are more firmlyattached to the overcoat layer with an increase in affinity between thetoner starting particles and the overcoat composition. Therefore, theovercoat composition used in the present invention is preferably thatwhich dissolves or swells the toner starting particles.

In the present invention, when lightness L1, chromaticity a1 andchromaticity b1 according to the L*a*b* color system of the fixed imageformed with at least two toners as well as lightness L2, chromaticity a2and chromaticity b2 according to the L*a*b* color system of the fixedimage obtained after the overcoat composition is dropped at 0.4 mg/cm²from a height of 10 mm above the fixed image and the overcoatcomposition is removed after 10 seconds have passed are applied to thefollowing formula (1), a color difference ΔE* is from 3.0 to 30.0,preferably from 4.0 to 20.0 and more preferably from 4.0 to 10.0:ΔE*=[(a2−a1)²+(b2−b1)²+(L2−L1)²]^(1/2)  (1).

Where the color difference ΔE* is less than 3.0, the overcoat layer maybe inferior in attachment property. Where the color difference ΔE* is inexcess of 30.0, there is a case that the overcoat composition may allowa fixed image to dissolve, thereby disturbing the image. The colordifference which is in the above-described preferable range isadvantageous in providing better attachment property. That is, where theovercoat composition is in a range at which the toner starting particlescan melt appropriately, the image is not disturbed and the overcoatlayer is excellent in attachment property.

More specifically, it is possible to determine the color difference ΔE*by the following procedure.

The color image forming apparatus is used to form a red-color fixedsolid image by overlapping two color toners, that is, magenta toner andyellow toner, on an OHP (overhead projector) sheet as a recordingmedium. The OHP sheet on which the red-color fixed solid image has beenformed is sandwiched with another OHP sheet and a spectroscopicdensitometer (X-Rite 938 made by X-Rite Inc.) is used to measurelightness L1, chromaticity a1 and chromaticity b1 of the fixed imageaccording to the L*a*b* color system (before titration). It is notedthat the OHP sheet is sandwiched as described above to keep thespectroscopic densitometer (X-Rite 938 made by X-Rite Inc.) clean.

Next, a fusion tester shown in FIG. 7 is used to put an overcoatcomposition 114 into a dropping burette 113 and the overcoat compositionis set so as to be 10 mm in height above the red-color fixed solid imageformed on an OHP sheet 112 placed on a titration base 111. Next, theovercoat composition 114 is dropped at a quantity of 0.4 mg and amicrowipe MU-2000 (made by MCC Co., Ltd.) is used to remove the overcoatcomposition 114 after 10 seconds have passed. The OHP sheet on which thered-color fixed solid image has been formed is sandwiched with anotherOHP sheet and the spectroscopic densitometer (X-Rite 938 made by X-RiteInc.) is used to determine lightness L2, chromaticity a2 andchromaticity b2 of the fixed image according to the L*a*b* color system(after titration). These measured values are applied to the followingformula (1), thus making it possible to calculate a color difference ΔE*before and after titration of the overcoat composition.ΔE*=[(a2−a1)²+(b2−b1)²+(L2−L1)²]^(1/2)  (1)

Further, the inventors have studied in detail a phenomenon in which theovercoat composition is repelled on the oilless fixed image and havefound that spots liable to repel the overcoat composition are notpresent uniformly but a solid image part where an image is present andalso great in image area is liable to repel the overcoat composition.Thus, an electron microscope is used to observe a cross section of thesolid image part which has been subjected to oilless fixing, therebyrevealing that a releasing agent (wax) of toner covers the surface ofthe image substantially in its entirety.

It has been also found that a spot which has an overcoat layer on anoilless fixed image and is liable to detachment of the overcoat layer isa spot which has an image, and solid image parts great in quantity oftoner adhered (in particular, red, blue and green spots) are liable todetachment most easily. Therefore, observations by using an electronmicroscope have been carried out for a boundary surface between a solidimage part having an overcoat layer at a solid image part of the imagewhich has been subjected to oilless fixing and the overcoat layer. Ithas been revealed that there is a spot having wax on the boundarysurface between the solid image part and the overcoat layer, and in aspot having the wax, such a spot is present that the overcoat layer isslightly afloat. That is, it has been found that the larger the numberof spots at which the wax is in contact with the overcoat layer, thegreater the attachment property of the overcoat layer to the oillessfixed image is decreased.

Wax involved in the attachment property of the oilless fixed image tothe overcoat layer is distributed on the outermost surface of theoilless fixed image, and wax present inside the image is not involved.Therefore, evaluation has been made for whether the oilless fixed imageon which the overcoat layer is favorably provided can be regulated ornot with reference to a distribution state of the wax on the outermostsurface of the oilless fixed image.

Here, as techniques for observing an inner structure of a polymer, whenobservations are carried out by using a transmission electron microscope(TEM), a section of a polymer is treated with osmium tetroxide (K. Kato:Polym. Eng. Sci., 7, 38), ruthenium tetroxide (J. S Trent et al.:Macromolecules, 16, 589), tungstophosphoric acid (K. Hess et al.:Kalloid-Z, 168, 37), etc.

Chemical modification is effected in a different manner depending oneach polymer and a substance which effects chemical modificationcontains a heavy metal. Since electrons are less likely to transmit, achemically modified polymer is observed darkly, while a polymer which isnot chemically modified is observed brightly. The above-describedsubstances are generally used in techniques for imparting contrast to aTEM image. Of the substances, ruthenium tetroxide can be applied to manypolymer materials, and is therefore preferable.

Evaluation has been made for whether a site having wax can bedistinguished from a site free of wax in an image (SEM image) taken by ascanning electron microscope when an oilless fixed image is chemicallymodified by ruthenium tetroxide, with attention given to the fact thattoner starting particles containing a binding resin such as polyesterand polystyrene are easily chemically modified by ruthenium tetroxideand the wax is by far less likely to be chemically modified by rutheniumtetroxide than the toner starting particles. That is, Ru which is astructural element of ruthenium tetroxide is much larger in atomicnumber than hydrogen, carbon, nitrogen and oxygen which are structuralelements of the oilless fixed image. Therefore, in the SEM image, suchcharacteristics can be utilized that reflection electrons or secondaryelectrons from a sample are increased in quantities with an increase inthe atomic number of elements.

Further, since ruthenium tetroxide modifies only the outermost surfaceof the sample, it is necessary that a depth region to be observed by ascanning electron microscope (SEM) is the outermost surface to theextent possible.

It is generally known that on SEM observations, the depth of a sample tobe observed depends on accelerating voltage. When accelerating voltageis applied at 1 kV or less, it is possible to observe only informationon the depth of dozens of nm or less.

On the basis of the above-described findings, after the oilless fixedimage is treated with vapor of ruthenium tetroxide, reflection electronsare used to observe the surface of the fixed image, with theaccelerating voltage of the SEM kept at 0.8 kV. It has been found that apart having wax is dark, while a part free of wax is bright inobservation.

It has been also found that an area percentage of the dark part of theSEM image (reflection electron image) can be handled as a coveragefactor of wax on the outermost surface of the oilless fixed image, andthe coverage factor of wax on the outermost surface of the oilless fixedimage can be referenced to regulate an oilless fixed image on which anovercoat layer can be favorably provided.

Therefore, in the present invention, when at least any one of red, greenand blue fixed solid images formed with at least two toners using a testchart No. 4 according to ISO/IEC 15775:1999 is exposed to saturatedvapor of an aqueous ruthenium tetroxide solution and is then radiatedwith electron beams at accelerating voltage of 0.8 kV to obtain areflection electron image and the reflection electron image is convertedto a binarization image formed of a black part and a white part, an areapercentage of the black part with respect to an entire area of thebinarization image (sometimes referred to as “wax coverage factor”) ispreferably from 40% to 70% and more preferably from 42% to 65%. Wherethe wax coverage factor is less than 40%, there is a case that the moldreleasability of an image from a fixing roller may be decreased toresult in a failure of obtaining a high quality image. Where the waxcoverage factor is in excess of 70%, there is a case that the overcoatlayer may be decreased in attachment property.

It is noted that where an image forming apparatus for a color image isused to form a black-and-white image, the black-and-white image is from30% to 60% in wax coverage factor.

-Chemical Modification-

In a method for determining the wax coverage factor, there is noparticular restriction on the concentration of ruthenium tetroxide onexposure of the surface of the oilless fixed image to saturated vapor ofan aqueous ruthenium tetroxide solution, as long as ruthenium tetroxidecan be chemically modified safely and at a high reproducibility. Forexample, 5% by mass of an aqueous ruthenium tetroxide solution which iscommercially available as an electron microscope reagent (made by TABBInc. (England)) is used to chemically modify ruthenium tetroxide stably,and is therefore preferable.

When the aqueous ruthenium tetroxide solution is kept in a sealed space,ruthenium tetroxide will volatilize into saturated vapor. Therefore, anoilless fixed image is placed in the sealed space, thus making itpossible to chemically modify the oilless fixed image easily withruthenium tetroxide.

Here, the saturated vapor of the aqueous ruthenium tetroxide solutionmay be exposed at a room temperature. For example, temperatures of 15°C. to 35° C. are preferable and 18° C. to 30° C. are more preferable.

There is no particular restriction on the exposure time to the masaturated vapor of the aqueous ruthenium tetroxide solution, as long asthe oilless fixed image is chemically modified reliably and can beclearly separated from a releasing agent on SEM observations. Theexposure time is preferably from 3 minutes to 8 minutes and morepreferably from 4 minutes to 6 minutes.

Where the exposure time is less than 3 minutes, there is a case that theoilless fixed image may not be chemically modified sufficiently and thefixed image may not be clearly separated from the releasing agent, whichis not preferable. On the other hand, where the exposure time is inexcess of 8 minutes, ruthenium tetroxide adheres on the surface of thereleasing agent as well. And, there is a case that a dark part observedin a SEM image may be increased in percentage or a boundary between aspot having a releasing agent and a spot free of the releasing agent maynot be clearly distinguished.

-SEM Observations-

When a scanning electron microscope (SEM) is used to observe the surfaceof an oilless fixed image treated with ruthenium tetroxide, it is foundthat a part having wax is dark and a part free of wax is bright inobservation. At this time, accelerating voltage is preferably from 0.3kV to 1.0 kV and more preferably from 0.5 kV to 0.9 kV.

Where the accelerating voltage is in excess of 1.0 kV, information isdetected from a site at which the oilless fixed image is deep.Therefore, when wax adheres thinly, information is collected from thesurface of the oilless fixed image chemically modified by rutheniumtetroxide through the wax. In the present invention, the acceleratingvoltage is applied at 0.8 kV, thus making it possible to observe aregion of the outermost surface on which the wax is present at a highreproducibility.

Where SEM observations are carried out for the oilless fixed image whichhas been treated with ruthenium tetroxide, it is found that a sitehaving wax is dark and a site free of wax is bright in observation bothin a secondary electron image and a reflection electron image. Thus, thesite having wax can be distinguished from the site free of wax moreclearly in the reflection electron image.

This is due to the fact that the reflection electrons and the secondaryelectrons are increased in quantity with an increase in the atomicnumber of elements. The reflection electrons are produced in a greaterquantity than the secondary electrons, depending on an increase in theatomic number. As a result, in the reflection electron image, a sitehaving wax is darker and a site free of wax is brighter to such anextent that can eliminate irregularity information kept by the oillessfixed image, and this is preferable.

In this case, FIG. 1A shows an oilless fixed image which is poorlyattached to an overcoat layer. FIG. 2A shows an oilless fixed imagewhich is favorably attached to an overcoat layer.

As shown in a reflection electron image obtained by chemically modifyingan oilless fixed image with ruthenium tetroxide to carry out,thereafter, SEM observations of the oilless fixed image at acceleratingvoltage of 0.8 kV, it is apparent that the poorly attached oilless fixedimage in FIG. 1A is dark in its entirety and quite small in the numberof bright spots. Meanwhile, it is apparent that the favorably attachedoilless fixed image in FIG. 2A is bright in its entirety and small inthe number of dark spots.

The reflection electron image is observed at any magnificationappropriately selected depending on how wax is present. There is noparticular restriction on the magnification, as long as observations arecarried out for a region having toner. The magnification is preferablyfrom ×100 to ×2,000.

-Binarization Processing-

There is carried out image processing (binarization) in which individualpixels (or a predetermined number of pixel units) which configure anobtained reflection electron image (image data) are classified into apart that looks black (black part) and a part that looks white (whitepart) to obtain a binarization image. FIG. 1B shows a binarization imageof FIG. 1A. FIG. 2B shows a binarization image of FIG. 2A.

In effecting binarization, it is acceptable that brightness isdetermined, for example, for each pixel and where the brightness is at acertain value (threshold value) or more, the white part is given andwhere the brightness is less than a certain value, the black part isgiven. Further, the threshold value is set with reference to a histogramof brightness.

-Calculation of Area Percentage of Black Part-

Next, calculation is made for an area percentage of a black part withrespect to an entire binarization image on the basis of a reflectionelectron image. It is acceptable that the calculation is made, forexample, by arithmetic processing in which an entire area of thebinarization image and an area of the black part are determined todivide the area of the black part by the entire area of the binarizationimage or the calculation is made by arithmetic processing in which thenumber of pixels (number of dots) of the black part is divided by thenumber of pixels of the entire binarization image.

Here, in the reflection electron image, a region having wax looks black,while a region free of wax looks white. It can be, therefore, thoughtthat the area percentage of the black part with respect to the entirebinarization image is a wax coverage factor.

In the oilless fixed image, it is preferable to regulate the waxcoverage factor of a spot which is greatest in toner adhesion quantity.

In the image forming method of the present invention which uses anoilless fixing method, an exclusive source of wax which deteriorates theattachment property of an oilless fixed image to an overcoat layer istoner. Therefore, in the oilless fixed image, a site which is greatestin wax content is a spot at which the toner adheres in a great quantity,that is, a solid part of the image.

In formation of an electrophotographic image, four different colortoners of black, magenta, cyan and yellow are used to reproduce variouscolors. Therefore, in a solid image of the oilless fixed image, red,blue and green spots are those where the toners adhere in a greaterquantity than a black spot and also greater in content of wax.

In the present invention, at least any one of red, green and blue fixedsolid images formed with at least two toners using a test chart No. 4according to ISO/IEC 15775:1999 is exposed to saturated vapor of anaqueous ruthenium tetroxide solution and is then radiated with electronbeams at accelerating voltage of 0.8 kV to obtain a reflection electronimage and the reflection electron image is converted to a binarizationimage formed of a black part and a white part. Where an area percentageof the black part with respect to an entire area of the binarizationimage (“wax coverage factor”) is from 40% to 70%, the attachmentproperty to the overcoat layer is favorable and a high-grade beautifulimage is obtained.

The wax coverage factor will vary in accordance with the content of waxin toner, a distribution state and types of wax. The lower the contentof wax in the toner, the lower the wax coverage factor becomes. Thegreater the wax in the toner is available in the vicinity of the surfaceof the toner, the higher the wax coverage factor becomes. Further, anoilless fixed image is further increased in wax coverage factor as thereis used wax which is lower in melting point and higher in flowability.

The wax coverage factor of the oilless fixed image will also vary inaccordance with an adhesion quantity of toner. The lower the adhesionquantity of the toner, the lower the wax coverage factor becomes. In animage on which an overcoat layer is provided, the surface of the imagebecomes flat. Therefore, the image is taken as being denser than usual,and the adhesion quantity of the toner can be decreased to lower the waxcoverage factor.

Further, the wax coverage factor of the oilless fixed image also variesdepending on fixing conditions. As a matter of course, the higher thefixing temperature, the longer the image is heated by a fixing rollerand the higher the pressure of the fixing roller is, the higher the waxcoverage factor of the oilless fixed image becomes.

As described so far, many factors are found by which the wax coveragefactor of the oilless fixed image varies. However, the wax coveragefactor of the oilless fixed image can be easily set at a substantiallyconstant value, if individual conditions are defined. Therefore, ahigh-grade and beautiful image great in durability can be obtained byproviding an overcoat layer on the image.

<Electrostatic Latent Image Forming Step and Electrostatic Latent ImageForming Unit>

The electrostatic latent image forming step is a step of forming anelectrostatic latent image on an electrostatic latent image bearingmember and carried out by an electrostatic latent image forming unit.

The electrostatic latent image bearing member (which may be hereinafterreferred to as “electrophotographic photoconductor,” “photoconductor” or“image carrying body”) is not particularly restricted in terms of thematerial, shape, structure, size, or the like thereof and any of thementioned can be appropriately selected from those known in the art. Theelectrostatic latent image bearing member preferably has a drum-likeshape, and the examples of the material thereof include, for example,inorganic photoconductors such as amorphous silicone, selenium andorganic photoconductors (OPC) such as polysilane and phthalopolymethin.Of these materials, amorphous silicone and the like are preferable interms of an extended service life.

The electrostatic latent image can be formed, for example, by uniformlycharging the surface of the electrostatic latent image bearing memberand then exposing imagewise by means of the electrostatic latent imageforming unit.

The electrostatic latent image forming unit is provided at least with,for example, an electrification device for uniformly charging thesurface of the electrostatic latent image bearing member and an exposuredevice for exposing imagewise the surface of the electrostatic latentimage bearing member.

The charging can be performed by applying electric voltage to thesurface of the electrostatic latent image bearing member by using, forexample, the electrification device.

There is no particular restriction on the electrification device and anyelectrification device can be appropriately selected depending on thepurpose. The electrification device includes, for example, contact-typeelectrification devices known in the art and equipped with a conductiveor semi-conductive roller, a brush, a film, a rubber blade or the like,and non-contact type electrification devices which utilize coronadischarge such as corotron and scorotron.

Further, it is preferable that the electrification device is thatarranged in the electrostatic latent image bearing member in a contactor non-contact state and charges the surface of the electrostatic latentimage bearing member by superimposing and applying a direct currentvoltage and an alternating current voltage.

Still further, it is preferable that the electrification device is acharging roller which is arranged in the electrostatic latent imagebearing member in close proximity so as not to be in contact via a gaptape and the surface of the electrostatic latent image bearing member ischarged by superimposing and applying a direct current voltage and analternating current voltage to the charging roller.

The exposure can be performed by exposing imagewise the surface of theelectrostatic latent image bearing member by using, for example, theexposure device.

There is no particular restriction on the exposure device and anyexposure device can be appropriately selected depending on the purpose,as long as exposure can be conducted imagewise according to an image tobe formed on the surface of the electrostatic latent image bearingmember charged by the electrification device. For example, various typesof exposure devices are included such as a photocopy optical system, arod lens array system, a laser beam optical system, and a liquid crystalshutter optical system.

In the present invention, a back exposure system may be employed inwhich exposure is conducted imagewise from the backside of theelectrostatic latent image bearing member.

<Development Step and Development Unit>

The development step is a step of developing the electrostatic latentimage using at least two toners which contain a releasing agent and areselected from black toner, magenta toner, cyan toner and yellow toner toform a visible image and can be carried out by using a development unit.

There is no particular restriction on the development unit as long as animage can be developed by using, for example, at least two tonersselected from the black toner, the magenta toner, the cyan toner and theyellow toner and developers of the respective colors. Any developingunit can be appropriately selected from conventionally known units. Forexample, a developing unit which is at least provided with a developingdevice which houses the toners and developers of the respective colorsand which is capable of imparting the developers to the electrostaticlatent image in a contact or non-contact manner is cited.

The developing device may be a dry-type developing device, a wet-typedeveloping device, a single color developing device or a multi-colordeveloping device. For example, a developing device which has anagitator for frictionally agitating the developers to effect chargingand a rotatable magnet roller is cited.

Inside the developing device, for example, the toners of the respectivecolors and carriers are mixed and agitated, and the toners are chargedby the resulting friction and kept raised on the surface of a rotatingmagnet roller, thereby forming a magnetic brush. Since the magnet rolleris arranged in the vicinity of the electrostatic latent image bearingmember, the toners configuring the magnetic brush formed on the surfaceof the magnet roller are partially moved to the surface of theelectrostatic latent image bearing member due to an electrical suctionforce. As a result, the electrostatic latent image is developed with thetoners and a visible image is formed on the surface of the electrostaticlatent image bearing member with the toners.

<<Toners>>

The above-described toners include at least two toners selected fromblack toner, magenta toner, cyan toner and yellow toner.

Each of the respective color toners contains at least a releasing agent,preferably contains a binding resin and a coloring agent, and alsocontains other components, whenever necessary.

-Releasing Agent-

There is no particular restriction on the releasing agent and anyreleasing agent can be appropriately selected depending on the purpose.Preferable are waxes.

The waxes include, for example, natural waxes, synthesized waxes andother waxes.

The natural waxes include, for example, vegetable-based waxes such ascarnauba wax, cotton wax, haze wax, rice wax, animal-based waxes such asbee wax and lanolin, mineral-based waxes such as ozokerite and selsyn,and petroleum-based waxes such as paraffin wax, microcrystalline wax andpetrolatum wax.

The synthesized waxes include, for example, synthesized so hydrocarbonwaxes such as Fischer Tropsch wax, polyethylene and polypropylene,fat-based synthesized waxes such as ester, ketone and ether, andhydrogenated waxes.

Other waxes include, for example, fatty acid amide compounds such as12-hydroxy stearamide, stearamide, anhydrous phthalic acid imide andchlorinated hydrocarbon; homopolymers or copolymers of polyacrylate suchas poly-n-stearyl methacrylate, poly-n-lauryl methacrylate which arecrystalline high-polymer resins with low molecular weight (copolymersof, for example, n-stearyl acrylate-ethyl methacrylate or the like) andcrystalline high-polymer resins having a long alkyl group on a sidechain.

Of these waxes, preferable are paraffin wax, microcrystalline wax,Fischer Tropsch wax, polyethylene wax and polypropylene wax. Inparticular, preferable is microcrystalline wax in terms of moldreleasability.

The microcrystalline wax contains isoparaffin and cycloparaffin andcrystallizes in a relatively small size. Therefore, the wax is notuniformly present on an oilless fixed image but more likely to bepresent in a state of dispersion. As a result, the oilless fixed imagecan be decreased in wax coverage factor.

It is preferable in view of attachment property to an overcoatcomposition that the above-described wax contains isoparaffin which is ahydrocarbon component in 10% by mass or more.

There is no particular restriction on the weight-average molecularweight of the wax and any weight-average molecular weight can beappropriately selected depending on the purpose. The weight-averagemolecular weight is preferably 500 or more in view of attachmentproperty to the overcoat composition.

Here, isoparaffin content of the wax (% by mass) and weight-averagemolecular weight of the wax can be determined by using a gaschromatograph TOF-type mass spectrometer, for example, JMS-T100GC“AccuTOF GC” (made by JEOL Ltd.) according to a field desorption (FD)method.

There is no particular restriction on the melting point of the wax andany melting point can be appropriately selected depending on thepurpose. The melting point is preferably from 40° C. to 160° C. and morepreferably from 50° C. to 120° C. Where the melting point is less than40° C., there is a case that the heat resistant storage stability may beadversely influenced. Where the melting point is in excess of 160° C.,there is a case that cold offset may take place easily when an image isfixed at a low temperature.

Melting viscosity of the wax is preferably from 5 cps to 1,000 cps at atemperature which is 20° C. higher than the melting point and morepreferably from 10 cps to 100 cps. Where the melting viscosity is inexcess of 1,000 cps, there is a case that the hot offset resistance andfixing property at a low temperature may be improved to a lesser extent.

There is no particular restriction on the content of the wax in thetoner and any content can be appropriately selected depending on thepurpose. The content is preferably from 1% by mass to 40% by mass andmore preferably from 3% by mass to 30% by mass.

-Binding Resin-

There is no particular restriction on the binding resin and any bindingresin can be appropriately selected depending on the purpose. Thebinding resin includes, for example, styrene such as polystyrene, polyp-styrene, polyvinyl toluene, or a single polymer of its substitutethereof, a styrene-based copolymer such as styrene-p-chlorstyrenecopolymer, styrene-propylene copolymer, styrene-vinyl toluene copolymer,styrene-acrylic acid methyl copolymer, styrene-acrylic acid ethylcopolymer, styrene-meta acrylic acid copolymer, styrene-meta acrylicacid methyl copolymer, styrene-meta acrylic acid ethyl copolymer,styrene-meta acrylic acid butyl copolymer, styrene-α-chlormeta acrylicacid methyl copolymer, styrene-acrylonitrile copolymer,styrene-vinylmethyl ether copolymer, styrene-vinyl methylketonecopolymer, styrene-butadiene copolymer, styrene-isopropyl copolymer,styrene-maleic acid ester copolymer; polymethyl methacrylate resin,polybutyl methacrylate resin, polyvinyl chloride resin, polyvinylacetate resin, polyethylene resin, polyester resin, polyurethane resin,epoxy resin, polyvinyl butyral resin, polyacrylic resin, rosin resin,modified rosin resin, terpene resin, phenol resin, aliphatic or aromatichydrocarbon resin, aromatic petroleum resin. They may be used solely orin combination of two or more of them. Of these resins, in particular,preferable is polyester resin in view of an affinity with a recordingmedium to be fixed.

Components which configurate the polyester resin include, for example, adivalent alcohol component, a trivalent or higher multivalent alcoholcomponent and an acid component.

The divalent alcohol component includes, for example, ethylene glycol,propylene glycol, 1,3-butane diol, 1,4-butane diol, 2,3-butane diol,diethylene glycol, triethylene glycol, 1,5-pentane diol, 1,6-hexanediol, neopentyl glycol, 2-ethyl-1,3-hexane diol, hydrogenated bisphenolA, and diol obtained by polymerization of bisphenol A by cyclic ethersuch as ethylene oxide and propylene oxide.

The trivalent or higher multivalent alcohol component includes, forexample, sorbitol, 1,2,3,6-hexane tetrol, 1,4-sorbitan, pentaerythritol,dipentaerythritol, tripenta erythritol, 1,2,4-butane triol,1,2,5-pentatriol, glycerol, 2-methylpropane triol, 2-methyl-1,2,4-butanetriol, trimethylol ethane, trimethylol propane, and 1,3,5-trihydroxybenzene.

The acid component includes, for example, benzene dicarboxylic acid suchas phthalic acid, isophthalic acid, terephthalic acid or its anhydride;alkyl dicarboxylic acid such as succinic acid, adipic acid, sebacicacid, azelaic acid or its anhydride; unsaturated diprotic acid such asmaleic acid, citraconic acid, itaconic acid, alkenyl succinic acid,fumaric acid and mesaconic acid; unsaturated diprotic acid anhydridesuch as maleic acid anhydride, citraconic acid anhydride, itaconic acidanhydride and alkenyl succinic acid anhydride; and trivalent or highermultivalent carboxylic acid components.

The trivalent or higher multivalent carboxylic acid component includes,for example, trimellitic acid, pyromellitic acid, 1,2,4-benzenetricarboxylic acid, 1,2,5-benzene tricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalene tricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexane tricarboxylic acid,1,3-dicarboxy-2-methyl-2-methylene carboxypropane, tetra(methylenecarboxy)methane, 1,2,7,8-octane tetracarboxylic acid, EnPol trimer acidor their anhydrides, and partially lower alkyl ester.

-Modified Polyester Capable of Reacting with Active HydrogenGroup-Containing Compound-

The binding resin may contain a modified polyester (prepolymer) capableof reacting with an active hydrogen group-containing compound. Theactive hydrogen group-containing compound acts as an elongating agentand a cross-linking agent, when the modified polyester capable ofreacting with the active hydrogen group-containing compound undergoeselongation reaction or cross-linking reaction in the process ofproducing toners. The modified polyester capable of reacting with theactive hydrogen group-containing compound undergoes elongation reactionto increase in molecular weight, thereby, making it possible toeffectively increase the heat resistant storage stability of toner andsuppress an image from being sticky after the fixing step. In this case,there is no particular restriction on the modified polyester capable ofreacting with the active hydrogen group-containing compound as long asit is capable of reacting with the active hydrogen group-containingcompound. Any modified polyester can be appropriately selected dependingon the purpose and includes, for example, a modified polyester whichcontains an isocyanate group, epoxy group, carboxylic acid, acidchloride group. Of these modified polyesters, preferable is a modifiedpolyester which contains an isocyanate group.

There is no particular restriction on the active hydrogengroup-containing compound as long as it contains an active hydrogengroup. Any active hydrogen group-containing compound can beappropriately selected depending on the purpose. Where the modifiedpolyester capable of reacting with the active hydrogen group-containingcompound is a modified polyester which contains an isocyanate group,amines are preferable because they can be increased in molecular weightdue to elongation reaction or cross-linking reaction with the isocyanategroup-containing modified polyester.

There is no particular restriction on the amines and any amines can beappropriately selected depending on the purpose. The amines include, forexample, phenylene diamine, diethyltoluene diamine, 4,4′-diaminodiphenylmethane, 4,4′-diamino-3,3′-dimethyl dicyclohexyl methane, diaminecyclohexane, isophorone diamine, ethylene diamine, tetramethylenediamine, hexamethylene diamine, diethylene triamine, triethylenetetramine, ethanol amine, hydroxyethyl aniline, aminoethyl mercaptan,amonopropyl mercaptan, aminopropionic acid, and aminocapronic acid. Theamines also include ketimine compounds in which amino groups of theamines are blocked with ketones (such as acetone, methylethyl ketone,methylisobutyl ketone) and oxazolizone compounds.

-Coloring Agent-

There is no particular restriction on the coloring agents and anycoloring agents can be appropriately selected depending on the purpose.They include, for example, carbon black, nigrosin dye, black iron oxide,naphthol yellow S, hansa yellow (10G, 5G, C), cadmium yellow, yellowiron oxide, Chinese yellow, chrome yellow, titan yellow, polyazo yellow,oil yellow, hansa yellow (GR, A, RN, R), pigment yellow L, benzidineyellow (G, GR), permanent yellow (NCG), Vulcan fast yellow (5G, R),tartrazine lake, quinoline yellow lake, anthrazane yellow BGL,isoindolinone yellow, red iron oxide, red lead, red vermilion, cadminumred, cadminum mercury red, antmony red, permanent red 4R, para red, firered, para-chloro-ortho-nitroaniline red, lithol fast scarlet G,brilliant fast scarlet, brilliant carmine BS, permanent red (F2R, F4R,FRL, FRLL, F4RH), fast scarlet VD, Vulcan fast rubine B, brilliantscarlet G, lithol rubine GX, permanent red FSR, brilliant carmine 6B,pigment scarlet 3B, Bordeaux 5B, toluidine maroon, permanent BordeauxF2K, helio Bordeaux BL, Bordeaux 10B, BON maroon light, BON maroonmedium, eosin lake, rhodamine lake B, rhodamine lake Y, alizarin lake,thioindigo red B, thioindigo maroon, oil red, quinacridone red,pyrazolone red, polyazo red, chrome vermilion, benzidine orange,perinone orange, oil orange, cobalt blue, cerulean blue, alkali bluelake, peacock blue lake, Victoria blue lake, metal-free phthalocyanineblue, phthalocyanine blue, fast sky blue, indanthrene blue (RS, BC),indigo, ultramarine blue, iron blue, anthraquinone blue, fast violet B,methyl violet lake, cobalt purple, manganese purple, dioxane violet,anthraquinone violet, chrome green, zinc green, chrome oxide, pyridiane,emerald green, pigment green B, naphthol green B, green gold, acid greenlake, malachite green lake, phtharocyanine green, anthraquinone green,titanium oxide, zinc white, and lithopone. They may be used solely or incombination of two or more of them.

There is no particular restriction on the content of the coloring agentand any content can be appropriately selected depending on the purpose.The content is preferably from 1 part by mass to 15 parts by mass withrespect to 100 parts by mass of the toner, and more preferably from 3parts by mass to 10 parts by mass.

The coloring agent may be used as a master batch synthesized with aresin. There is no particular restriction on the resin and any resin canbe appropriately selected from known resins depending on the purpose.The resin includes, for example, styrene or a polymer of a substitutethereof, styrene-based copolymer, polymethyl methacrylate resin,polybutyl methacrylate resin, polyvinyl chloride resin, polyvinylacetate resin, polyethylene resin, polypropylene resin, polyester resin,epoxy resin, epoxypolyol resin, polyurethane resin, polyamide resin,polyvinyl butyral resin, polyacrylic resin, rosin, modified rosin,terpene resin, aliphatic hydrocarbon resin, alicyclic hydrocarbon resinand aromatic petroleum resin. They may be used solely or in combinationof two or more of them.

<Other Components>

There is no particular restriction on the other components and any othercomponents can be appropriately selected depending on the purpose. Theyinclude, for example, a charge control agent, a magnetic material and anexternal additive.

-Charge Control Agent-

There is no particular restriction on the charge control agent. Apositive or negative charge control agent can be appropriately selectedto use depending on whether a photoconductor is charged positively ornegatively.

The negative charge control agent includes, for example, a resin or acompound which has an electron donor functional group, an azo dye and anorganic acid metal complex.

Commercially available products of the negative charge control agentinclude, for example, Bontron (product No.: S-31, S-32, S-34, S-36,S-37, S-39, S-40, S-44, E-81, E-82, E-84, E-86, E-88, A, 1-A, 2-A, 3-A)(all of which are made by Orient Chemical Industries Ltd.); Kaya charge(product No.: N-1, N-2), Kaya set black (product No.: T-2, 004) (all ofwhich are made by Nippon Kayaku Co., Ltd.); Aizen Spilon black (T-37,T-77, T-95, TRH, TNS-2) (all of which are made by Hodogaya Chemical Co.,Ltd.); FCA-1001-N, FCA-1001-NB, FCA-1001-NZ (all of which are made byFujikura Kasei Co., Ltd.). They may be used solely or in combination oftwo or more of them.

The positive charge control agent includes, for example, a basiccompound such as nigosin dye; a cationic compound such as quaternaryammonium salt; a metal salt of higher fatty acid.

Commercially available products of the positive charge control agentinclude, for example, Bontron (product No.: N-01, N-02, N-03, N-04,N-05, N-07, N-09, N-10, N-11, N-13, P-51, P-52, AFP-B) (all of which aremade by Orient Chemical Industries Ltd.); TP-302, TP-415, TP-4040 (allof which are made by Hodogaya Chemical Co., Ltd.); Copy blue PR, Copycharge (product No.: PX-VP-435, NX-VP-434) (all of which are made byHoechst AG); FCA (product No.: 201, 201-B-1, 201-B-2, 201-B-3, 201-PB,201-PZ, 301) (all of which are made by Fujikura Kasei Co., Ltd.); PLZ(product No.: 1001, 2001, 6001, 7001) (all of which are made by ShikokuChemicals Corporation). They may be used solely or in combination of twoor more of them.

There is no particular restriction on the content of the charge controlagent and any content can be appropriately selected depending on, suchas, types of a binding resin and a toner producing method which includesa dispersion method. The content of the charge control agent ispreferably from 0.1 parts by mass to 10 parts by mass with respect to100 parts by mass of the binding resin and more preferably from 0.2parts by mass to 5 parts by mass. Where the content is in excess of 10parts by mass, there is a case that the charging property of toner maybe excessively large to reduce the effect of a charge control agent,thus resulting in an increased electrostatic suction force with adeveloping roller, thereby reducing the flowability of a developer andthe density of an image. Where the content is less than 0.1 parts bymass, there is a case that charging starts poorly to result ininsufficient charging quantity, which may easily affect a toner image.

-Magnetic Material-

The magnetic material includes, for example, (1) magnetic iron oxidesuch as magnetite, maghemite, ferrite or iron oxide which contains othermetal oxides; (2) metal such as iron, cobalt, nickel, or an alloy ofthese metals with those such as aluminum, cobalt, copper, lead,magnesium, tin, zinc, antimony, beryllium bismuth, cadmium, calcium,manganese, selenium, titanium, tungsten, vanadium, or (3) a mixturethereof.

The magnetic material includes, for example, Fe₃O₄, γ-Fe₂O₃, ZnFe₂O₄,Y₃Fe₅O₁₂, CdFe₂O₄, Gd₃Fe₅O₂, CuFe₂O₄, PbFer₂O, NiFe₂O₄, NdFe₂O,BaFe₁₂O₁₉, MgFe₂O₄, MnFe₂O₄, LaFeO₃, iron particles, cobalt particles,and nickel particles. They may be used solely or in combination of o ormore of them. Of these materials, particularly preferable are fineparticles of triiron tetroxide and γ-diiron trioxide.

There is no particular restriction on the content of the magneticmaterial and any content can be appropriately selected depending on thepurpose. The content is preferably from 10 parts by mass to 200 parts bymass with respect to 100 parts by mass of the binding resin and morepreferably from 20 parts by mass to 150 parts by mass.

The magnetic material can be used as a coloring agent as well.

-External Additive-

The external additive includes inorganic fine particles which impartflowability, heat resistant storage stability, developing properties,transfer properties, charging properties, etc., to the toner.

The inorganic fine particles include, for example, silica, titania,alumina, cerium oxide, strontium titanate, calcium carbonate, magnesiumcarbonate, and calcium phosphate. They also include silica fineparticles which are hydrophobized by silicone oil, hexamethyldisilazane,etc., and titanium oxide which is subjected to specific surfacetreatment.

The silica fine particles are commercially available and thecommercially available products include, for example, Aerosil (productNo.: 130, 200V, 200CF, 300, 300CF, 380, OX50, TT600, MOX80, MOX170,COK84, RX200, RY200, R972, R974, R976, R805, R811, R812, T805, 11202,VT222, RX170, RXC, RA200, RA200H, RA200HS, RM50, RY200, REA200) (all ofwhich are made by Nippon Aerosil Co., Ltd.); HDK (product No.: H20,H2000, H3004, H2000/4, H2050EP, H2015EP, H3050EP, KHD50), HVK2150 (allof which are made by Wacker Chemie GmbH); Carbosil (product No.: L-90,LM-130, LM-150, M-5, PTG, MS-55, H-5 HS-5, EH-5, LM-150D, M-7D, MS-75D,TS-720, TS-610, TS-530) (all of which are made by Cabot Corporation).They may be used solely or in combination of two or more of them.

There is no particular restriction on the content of the inorganic fineparticles and any content can be appropriately selected depending on thepurpose. The content is preferably from 0.1 parts by mass to 5.0 partsby mass with respect to 100 parts by mass of the toner and morepreferably from 0.8 parts by mass to 3.2 parts by mass.

The toner is preferably from 0.93 to 1.00 in average circularity whichis an average value of circularity SR expressed by the following formula1 and more preferably from 0.95 to 0.99. The average circularity is anindex which shows a degree of irregularity of toner. When the toner is acomplete sphere, the average circularity is 1.00, and the averagecircularity becomes a smaller value as the surface configuration of thetoner becomes more complicated.

<Formula 1>

Circularity SR=(circumferential length of circle, the area of which isequal to projected area of toner particle)/(circumferential length ofprojected image of toner particle)

Where the average circularity is in a range of 0.93 to 1.00, the surfaceof toner particles is smooth, and a contact area between toner particlesor a contact area between toner particles and a photoconductor is small,therefore, the toner particles are excellent in transfer properties.Further, since the toner particles are free of corners, a developer isagitated by a small torque inside a developing device, and agitation iscarried out stably to produce no abnormal image. Still further, noangulate toner is found in toner for forming dots. Thus, when arecording medium is brought into contact under pressure for transfer,the pressure is applied uniformly to the toner in its entirety forforming the dots and a void space due to defect of transferred coloringagents is less likely to occur. In addition, toner is not angulated,therefore, the toner is small in pulverization force and will not damageor wear the surface of the photoconductor.

The average circularity can be measured by using, for example, aflow-type particle image analyzer (FPIA-1000 made by SysmexCorporation).

The toner is preferably from 3 μm to 10 μm in volume average particlediameter and more preferably from 4 μm to 8 μm. Where the volume averageparticle diameter is less than 3 μm, there is a case that phenomena suchas a reduction in transfer efficiency and a reduction in blade cleaningproperties may easily occur. Where it is in excess of 10 μm, it may bedifficult to suppress scattered printing of letters and lines.

Here, the toner can be measured for its volume average particle diameterby, for example, a Coulter-counter method. A device for measuringparticle size distribution of the toner by the Coulter-counter methodincludes, Coulter-counter TA-II and Coulter Multisizer II (each of whichis made by Beckman Coulter Inc.).

<<Toner Producing Method>>

There is no particular restriction on the toner producing method and anytoner producing method can be appropriately selected depending on thepurpose. The method includes, for example, a pulverization method, apolymerization method (suspension polymerization method and emulsionpolymerization method) in which a monomer composition containing aspecific polymerizable monomer is directly polymerized in an aqueousphase, a method in which a specific binding resin solution is emulsifiedor dispersed in an aqueous medium, a method in which toner is dissolvedin a solvent to remove the solvent and effect pulverization, and amelting and spraying method.

-Pulverization Method-

The pulverization method is a method in which, for example, tonermaterials are melted and kneaded, thereafter, pulverized and classifiedto obtain the toner.

In the pulverization method, for the purpose of increasing the averagecircularity of the toner, it is acceptable that a mechanical impactforce is applied to the obtained toner to control the configuration ofthe toner. The mechanical impact force is applied to the toner by using,for example, machines such as Hybridizer and Mechanofusion.

In melting and kneading the toner material, the toner materials aremixed and the thus prepared mixture is placed into a melting/kneadingmachine for melting and kneading. The melting/kneading machine includes,for example, a monoaxial continuous kneader, a biaxial continuouskneader and a batch-type kneader using a roll mill. The melting/kneadingmachine is commercially available and the commercially available machineincludes, for example, a KTK-type biaxial extruder (made by Kobe SteelLtd.), a TEM-type extruder (made by Toshiba Machine Co., Ltd.), abiaxial extruder (made by KCK Co., Ltd.), a PCM-type biaxial extruder(made by Ikegai Corp.), and a co-kneader (made by Buss AG). It ispreferable that the above-described melting and kneading are carried outunder proper conditions so as not to cause cleavage of molecular chainsof a binding resin. More specifically, the melting and kneading arecarried out at a temperature which is determined with reference to asoftening point of the binding resin. Where the temperature isexcessively higher than the softening point, the molecular chains areexcessively cleaved. Where the temperature is excessively low,dispersion may not proceed.

In the pulverization process, a kneaded product obtained in the kneadingprocess is pulverized. In this pulverization, it is preferable that thekneaded product is first roughly pulverized and then finely pulverized.In this case, such a method is preferably employed that particles arepulverized by being made to collide against a collision plate in jetstreams, particles are pulverized by being made to collide with otherparticles in jet streams, or particles are pulverized at a narrow gapbetween a rotor which rotates mechanically and a stator.

In the classification, pulverized products obtained in the pulverizationprocess are classified and adjusted so as to produce particles having apredetermined particle diameter. The classification can be carried outby using, for example, a cyclone, a decanter, or a centrifugal machineto remove fine particle portions.

After completion of the pulverization and classification, pulverizedproducts are classified into streams by a centrifugal force or the like,thereby producing toner with a predetermined particle diameter.

-Suspension Polymerization Method-

In the suspension polymerization method, a coloring agent, a releasingagent, etc., are dispersed in an oil-soluble polymerization initiatorand a polymerizable monomer, and a resultant thereof is emulsified anddispersed in an aqueous medium which contains a surfactant., a soliddispersing agent, etc., by an emulsion polymerization method to bedescribed later. Thereafter, the resultant is subjected topolymerization reaction and granulated to obtain the toner.

The polymerization monomer includes, for example, acids such as acrylicacid, methacrylic acid, α-cyanoacrylic acid, α-cyanomethacrylic acid,itaconic acid, crotonic acid, fumaric acid, maleic acid and anhydrousmaleic acid; acrylamide, methacrylamide, diacetone acrylamide or amethylol compound thereof; acrylate or methacrylate having amino groupssuch as vinylpyridine, vinylpyrolidone, vinylimidazole, ethyleneimine,and dimethylaminoethyl methacrylate. By partially using these, afunctional group can be introduced into the surface of toner particles.

Further, a dispersing agent to be used is selected from those that havean acid group or a basic group, by which the dispersing agent isadsorbed and allowed to remain on the surface of the toner, by which afunctional group can be introduced.

-Emulsion Polymerization Method-

In the emulsion polymerization method, a water-soluble polymerizationinitiator and a polymerizable monomer are emulsified in water by using asurfactant to synthesize latex by an ordinary emulsion polymerizationtechnique. A dispersion prepared by dispersing a coloring agent, areleasing agent, etc., in an aqueous medium is provided independently,the dispersion is mixed and, thereafter, aggregated into a toner size,heated and fused to obtain the toner. Use of a monomer which is similarto that used in the suspension polymerization method as latex enables tointroduce a functional group into the surface of the toner.

-Method for Emulsifying or Dispersing a Specific Binding Resin Solutioninto an Aqueous Medium-

A method for emulsifying or dispersing a specific binding resin solutioninto the aqueous medium is such that a solution or dispersion solutionof toner materials which contains at least a binding resin is emulsifiedor dispersed in the aqueous medium to prepare an emulsion solution ordispersion solution and, thereafter, toner is granulated (granulation inwater). This method is formed of the following processes of [1] to [4],for example.

Process [1]: Preparation of Solution or Dispersion Solution of TonerMaterials

A solution or dispersion solution of the toner materials is prepared bydissolving or dispersing the toner materials such as a coloring agentand a binding resin in an organic solvent. The organic solvent isremoved on granulation of toner or after granulation thereof.

Process [2]: Preparation of Aqueous Medium

There is no particular restriction on the aqueous medium and any aqueousmedium can be appropriately selected from known aqueous media. Theaqueous medium includes, for example, water, alcohol mixable with thewater, solvents such as dimethyl formaldehyde, tetrahydrofuran,cellosolves and lower ketones, or a mixture thereof. Of these media,water is particularly preferable.

The aqueous medium can be prepared by dispersing, for example, adispersion stabilizing agent such as resin fine particles in the aqueousmedium. There is no particular restriction on the quantity of the resinfine particles added to the aqueous medium, and any quantity can beappropriately selected depending on the purpose. The quantity ispreferably from 0.5% by mass to 10% by mass.

There is no particular restriction on the resin fine particles as longas a resin is able to form an aqueous dispersion solution in an aqueousmedium. The resin can be appropriately selected from known resins,including thermoplastic resins and thermosetting resins, for example,vinyl resin, polyurethane resin, epoxy resin, polyester resin, polyamideresin, polyimide resin, silicon resin, phenol resin, melamine resin,urea resin, aniline resin, ionomer resin, and polycarbonate resin. Theymay be used solely or in combination of two or more of them. Of theseresins, preferable is such a resin that is formed at least with one typeof those selected from vinyl resin, polyurethane resin, epoxy resin andpolyester resin in view of high availability of an aqueous dispersionsolution of resin fine particles in the shape of fine spheres.

Further, in the aqueous medium, it is preferable to use a dispersingagent in view of the fact that oil droplets of the solution or thedispersion solution are made stable on emulsification or dispersion tobe described later, whenever necessary, to obtain a desiredconfiguration and also make the particle size distribution sharp. Thereis no particular restriction on the dispersing agent, and any dispersingagent can be appropriately selected depending on the purpose. Thedispersing agent includes, for example, a surfactant, a poorwater-soluble inorganic compound dispersing agent, and a high molecularprotective colloid. They may be used solely or in combination of two ormore of them. Of these dispersing agents, in particular, preferable is asurfactant.

Process [3]; Emulsification or Dispersion

When the solution or the dispersion solution which contains the tonermaterials is emulsified or dispersed in the aqueous medium, it ispreferable that the solution or the dispersion solution which containsthe toner materials is dispersed, while being agitated in the aqueousmedium.

There is no particular restriction on the dispersion method, and anydispersion method can be appropriately selected depending on thepurpose. The dispersion method can be carried out by using, for example,a batch-type emulsifier such as a homogenizer (made by IKA GmbH),Polytron (made by Kinematica AG), TK Autohomo Mixer (made by PrimixCorporation); a continuous-type emulsifier such as Ebara Milder (made byEbara Corporation), TK Fill Mix, TK Pipeline Homomixer (made by PrimixCorporation), a colloid mill (made by Kobelco Eco-Solutions Co., Ltd.),Slasher, Trigonal wet-type pulverizer (made by Nippon Coke & EngineeringCo., Ltd.), Cavitron (made by Eurotec Ltd.), and Fine Flow Mill (made byPacific Machinery & Engineering Co., Ltd.); a high-pressure emulsifiersuch as Microfluodizer (made by Mizuho Industrial Co., Ltd.), Nanomizer(made by Nanomizer Inc.) and APV Gaulin (made by Gaulin Inc.), amembrane emulsifier such as a membrane emulsifier (made by Reika KogyoKK) a vibration-type emulsifier such as Vibro Mixer (made so by ReikaKogyo KK); and an ultrasonic emulsifier such as Ultrasonic Homogenizer(made by Branson Co., Ltd.). Of these machines, APV Gaulin, Homogenizer,TK Auto Homo Mixer, Ebara Milder, TK Fill Mix, and TK Pipeline Homomixerare, in particular, preferable in view of making the particle diameteruniform.

Where a modified polyester capable of reacting with an active hydrogengroup-containing compound is contained in the solution or the dispersionsolution as a binding resin, reactions proceed during emulsification ordispersion. There is no particular restriction on the reactionconditions. Any conditions can be appropriately selected depending oncombination of a polymer capable of reacting with the active hydrogengroup-containing compound and the active hydrogen group-containingcompound. Reaction time is preferably from 10 minutes to 40 hours, andmore preferably from 2 hours to 24 hours.

Process [4]: Removal of Solvent

Then, an organic solvent is removed from an emulsified slurry obtainedby the emulsification or dispersion. The organic solvent is removed by,for example, (1) a method in which a reaction system in its entirety isgradually heated to completely remove the organic solvent in oildroplets, and (2) emulsified dispersions are sprayed into a dryatmosphere to completely remove a non-water-soluble organic solvent inoil droplets, thereby forming toner fine particles and also removing anaqueous dispersing agent through evaporation.

<Transfer Step and Transfer Unit>

The transfer step is a step in which the visible image is transferred toa recording medium. Preferable is an aspect in which an intermediatetransfer member is used to primarily transfer a visible image on theintermediate transfer member and thereafter the visible image issecondarily transferred on the recording medium. More preferable is anaspect formed of a primary transfer step in which at least two colortoners are used or preferably a full color toner is used as the toner totransfer a visible image on an intermediate transfer member to form acomposite transferred image and a secondary transfer step in which thecomposite transferred image is transferred on a recording medium.

The transfer can be carried out by procedures in which, for example, thevisible image is transferred with a transfer/electrification device tocharge the electrostatic latent image bearing member and can be carriedout by means of the transfer unit. A preferable aspect of the transferunit is provided with a primary transfer unit for transferring a visibleimage on an intermediate transfer member to form a composite transferredimage and a secondary transfer unit for transferring the compositetransferred image on a recording medium.

There is no particular restriction on the intermediate transfer memberand any intermediate transfer member can be appropriately selected fromknown transfer bodies depending on the purpose. The intermediatetransfer member includes, for example, a transfer belt.

It is preferable that the transfer unit (the primary transfer unit andthe secondary transfer unit) is at least provided with a transfer devicefor detaching and charging the visible image formed on the electrostaticlatent image bearing member to the side of the recording medium. Thetransfer unit may be provided in one unit or two or more units.

The transfer device includes, for example, a corona transfer device bycorona discharge, a transfer belt, a transfer roller, a pressuretransfer roller and an adhesive transfer device.

There is no particular restriction on the recording medium as long as itis able to fix the toner. Any recording medium can be appropriatelyselected depending on the purpose.

There is no particular restriction on an embodiment of the recordingmedium and any embodiment can be appropriately selected depending on thepurpose. The embodiment includes a three-dimensional object having aflat face and a curved face other than a sheet form. The recordingmedium may include, for example, a medium such as paper on whichtransparent toner is uniformly fixed to protect the surface of the paper(so-called varnish coat). There is no particular restriction on thematerial of the recording medium and any material can be appropriatelyselected depending on the purpose. The material includes, for example,generally available fiber which configures paper, cloth, etc., a plasticfilm such as an OHP sheet having a liquid transmission layer, metal,resin and ceramic.

<Fixing Step and Fixing Unit>

The fixing step is a step in which a fixing member having no releasingagent on a surface thereof is used to fix a transferred image on arecording medium. The fixing step may be carried out for every transferof the image to the recording medium in using individual color toners ormay be carried out at the same time, with the image being laminated inusing the individual color toners.

There is no particular restriction on the fixing member as long as it isan oilless fixing member having no releasing agent on a surface thereof.Any fixing member can be appropriately selected depending on thepurpose. Preferable is a known heat pressure unit. The heat pressureunit includes a combination of a heating roller and a pressure rollerand a combination of a heating roller, a pressure roller and an endlessbelt.

The fixing member is preferably a unit which is provided with a heatingbody having a heating element, a film in contact with the heating bodyand a pressure member in contact with the heating body via the filmunder pressure, in which a recording medium having an unfixed imagethereon is made to pass between the film and the pressure member,thereby heating and fixing the image. The heat pressure unit conductsheating usually at a temperature of 80° C. to 200° C.

<Overcoat Layer Forming Step and Overcoat Layer Forming Unit>

The overcoat layer forming step is a step in which an overcoat layer isformed on the fixed image by polymerizing an overcoat composition andcan be carried out by the overcoat layer forming unit.

<<Overcoat Composition>>

The overcoat composition contains a polymerizable unsaturated compoundand a surfactant. It is preferable that the composition contains apolymerizable oligomer and a photo-polymerization initiator and alsocontains other components such as a sensitizing agent and apolymerization prohibiting agent, whenever necessary.

-Polymerizable Unsaturated Compound-

There is no particular restriction on the polymerizable unsaturatedcompound and any polymerizable unsaturated compound can be appropriatelyselected depending on the purpose. The polymerizable unsaturatedcompound includes, for example, a mono-functional polymerizableunsaturated compound, a di-functional polymerizable unsaturatedcompound, a tri-functional polymerizable unsaturated compound andtetra-functional or higher polymerizable unsaturated compound.

The polyfunctional polymerizable unsaturated compound is greater incuring speed than the mono-functional polymerizable unsaturated compoundand more suitable for high-speed fixing but greater in volume shrinkage.A polymerizable unsaturated compound which shrinks greatly on curingreactions easily undergoes curling. It is, therefore, preferable to useto the extent possible a polymerizable unsaturated compound or a polymerthereof which is lower in volume shrinkage rate.

The polymerizable unsaturated compound is preferably 15% or less involume shrinkage rate.

The mono-functional polymerizable unsaturated compound includes, forexample, 2-ethylhexyl acrylate, 2-hydroxylethyl acrylate, 2-hydroxyethylacrylate, 2-hydroxypropyl acrylate, benzyl acrylate, phenylglycolmonoacrylate, cyclohexyl acrylate, ethylcarbitol acrylate,acryloylmorpholine, and ethoxydiethylene glycolacrylate.

The di-functional polymerizable unsaturated compound includes, forexample, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate,1,9-nonanediol diacrylate, tripropylene glycol diacrylate,tetraethyleneglycol diacrylate, bisphenol A ethylene oxide adductdiacrylate.

The tri-functional polymerizable unsaturated compound includes, forexample, trimethylolpropane triacrylate, pentaerythritol triacrylate,and tris(2-hydroxyethyl)isocyanurate triacrylate.

The tetra-functional or higher polymerizable unsaturated compoundincludes, for example, pentaerythritol tetraacrylate,ditrimethylolpropane tetraacrylate, dipentaerythritolhydroxypentaacrylate and dipentaerythritol hexaacrylate.

They may be used solely or in combination of two or more of them.

Of these compounds, particularly preferable are 1,6-hexanedioldiacrylate, ethylcarbitol acrylate and acryloylmorpholine, in view ofhigh fusion capacity (high affinity with a binding resin in toner).

At least one polymerizable unsaturated compound selected from theabove-described compounds of 1,6-hexanediol diacrylate, ethylcarbitolacrylate and acryloylmorpholine is preferably from 20% by mass to 60% bymass in content, and more preferably from 30% by mass to 50% by mass.Where the content is less than 20% by mass, there is a case that anovercoat layer may be poorly attached. Where the content is in excess of60% by mass, there is a possibility that before formation of theovercoat layer, an image may melt partially to disturb the image.

There is no particular restriction on the total content of thepolymerizable unsaturated compounds in the overcoat composition and anytotal content can be appropriately selected depending on the purpose.The total content is preferably from 35% by mass to 90% by mass, morepreferably from 45% by mass to 85% by mass and, in particular,preferably from 40% by mass to 75% by mass. Where the total content isless than 35% by mass, there is a case that the viscosity may beexcessively high. Where it exceeds 90% by mass, there is a case thatpoor curing may take place, the viscosity may be excessively low andflexibility after curing may be deteriorated. The total content which isin the particularly preferable range is advantageous in obtainingappropriate viscosity and curing properties or forming a coat layerafter curing.

-Polymerizable Oligomer-

There is no particular restriction on the polymerizable oligomer and anypolymerizable oligomer can be appropriately selected depending on thepurpose. The polymerizable oligomer includes, for example, polyesteracrylate oligomer, epoxyacrylate oligomer, urethaneacrylate oligomer anddiallylphthalate oligomer.

There is no particular restriction on the polyester acrylate oligomerand any polyester acrylate oligomer can be appropriately selecteddepending on the purpose. The polyester acrylate oligomer includes, forexample, acrylic acid ester of polyester polyol obtained frommultivalent alcohol and polybasic acid. The polyester acrylate oligomerexhibits excellent reactivity.

There is no particular restriction on the epoxy acrylate oligomer and anepoxy acrylate oligomer can be appropriately selected depending on thepurpose. The epoxy acrylate oligomer includes, for example, epoxyacrylates obtained by reactions of acrylic acid with bisphenol-typeepoxy, novolac-type epoxy and alicyclic epoxy. The epoxy acrylate isexcellent in hardness, flexibility and curing properties.

There is no particular restriction on the urethane acrylate oligomer andany urethane acrylate oligomer can be appropriately selected dependingon the purpose. The urethane acrylate oligomer includes, for example,urethane acrylate oligomers obtained by reaction of polyester polyol andpolyether polyol with acrylic ester having diisocyanate and a hydroxylgroup. A film which is flexible and strong can be provided by using theurethane acrylate oligomer.

The polymerizable oligomer may be used solely or in combination of twoor more of them.

There is no particular restriction on the content of the polymerizableoligomer in the overcoat composition and any content can beappropriately selected depending on the purpose. The content ispreferably from 5% by mass to 60% by mass, more preferably from 10% bymass to 50% by mass and, in particular, preferably from 20% by mass to45% by mass. Where the content is less than 5% by mass, there is a casethat poor curing may take place, the viscosity may be excessively low orthe flexibility after curing may be deteriorated. Where it is in excessof 60% by mass, there is a case that attachment property may bedeteriorated or the viscosity may be excessively high. The content whichis in the particularly preferable range is advantageous in obtainingappropriate viscosity, curing properties, flexibility of an overcoatlayer after curing and strength.

There is no particular restriction on P.I.I. (Primary Skin IrritationIndex) of the polymerizable unsaturated compound and the polymerizableoligomer and any P.I.I. is appropriately selected depending on thepurpose. The P.I.I. is preferably 1.0 or less. Where the P.I.I. is 5.0or more, there is a case that skin irritation is too strong to cause asafety problem.

Further, it is preferable that hue of the polymerizable unsaturatedcompound and that of the polymerizable oligomer are close to colorlessand transparent to the extent possible. The hue is preferably 2 or lessaccording to Gardner's Gray Scale. Where the hue is in excess of 2according to Gardner's Gray Scale, there is a case that an image portionmay change in color or a background portion may change in colorconspicuously.

-Surfactant-

The surfactant is allowed to be contained in the overcoat composition,thereby imparting adsorption to a boundary surface between toner and anovercoat composition or decreasing the surface tension of the overcoatcomposition to improve wettability.

There is no particular restriction on the surfactant and any surfactantcan be appropriately selected depending on the purpose. The surfactantincludes, for example, an anionic surfactant, a nonionic surfactant, asilicone surfactant and a fluoro surfactant.

The anionic surfactant includes, for example, sulfosuccinate,disulfonate, phosphate ester, sulphate, sulfonate, and a mixturethereof.

The nonionic surfactant includes, for example, polyvinyl alcohol,polyacrylic acid, isopropyl alcohol, acetylene-based diols, ethoxylatedoctylphenol, ethoxylated/branched secondary alcohol, perfluorobutanesulfonate and alkoxylated alcohol.

The silicone surfactant includes, for example, polyether-modifiedpolydimethylsiloxane.

There is no particular restriction on the content of the surfactant inthe overcoat composition and any content can be appropriately selecteddepending on the purpose. The content is preferably from 0.1% by mass to5% by mass and more preferably from 0.5% by mass to 3% by mass. Wherethe content is less than 0.1% by mass, there is a case that the overcoatcomposition may be deprived of wettability. Where the content is inexcess of 5% by mass, there is a case that the curing properties may beinhibited. The content which is in the more preferable range isadvantageous in improving the wettability of the overcoat composition.

Photo-polymerization Initiator-

There is no particular restriction on the photo-polymerization initiatorand any photo-polymerization initiator can be appropriately selecteddepending on the purpose. The photo-polymerization initiator includes,for example, benzophenone, benzoin ethyl ether, benzoin isopropyl etherand benzyl. The photo-polymerization initiator commercially availableand the commercially available product thereof includes, for example,Irgacure 1300, Irgacure 369, Irgacure 907 (made by Ciba SpecialtyChemicals Inc.) and Lucirin TPO (made by BASH GmbH).

When ultraviolet light is radiated to a mixture of the polymerizableoligomer or the polymerizable unsaturated compound with thephoto-polymerization initiator, the photo-polymerization initiatorproduces a radical as shown in the formulae (I) and (II) given below.The radical causes an addition reaction, by which the polymerizableoligomer or the polymerizable unsaturated compound undergoespolymerization double bond. The addition reaction produces furtherradicals. And, the radicals repeat the addition reaction, by which theother polymerizable oligomers or the other polymerizable unsaturatedcompounds undergo polymerization double bond. As a result,polymerization reactions proceed as shown in the formula (III) givenbelow.

(I) Hydrogen Atom Abstraction

(II) Photofragmentation

(III) Polymerization

It is preferable that the photo-polymerization initiator ischaracterized by being (i) high in absorption efficiency of ultravioletlight, (ii) highly soluble in the polymerizable oligomer or thepolymerizable unsaturated compound, (iii) low in odor, yellowdiscoloration and toxicity, and, (iv) free of dark reaction.

There is no particular restriction on the content of thephoto-polymerization initiator in the overcoat composition and anycontent can be appropriately selected depending on the purpose. Thecontent is preferably from 1% by mass to 10% by mass and more preferablyfrom 2% by mass to 5% by mass.

-Sensitizing Agent-

Where there is used the hydrogen atom abstraction-type ofbenzophenone-based photo-polymerization initiator as shown in theformula (I), use of only the photo-polymerization initiator may delayreactions. Thus, it is preferable that an amine-based sensitizing agentis used in combination to raise the reactivity. The amine-basedsensitizing agent is allowed to be contained therein, thereby providingsuch effects that hydrogen is supplied to the photo-polymerizationinitiator by hydrogen atom abstraction and reactions disturbed by oxygenin the atmosphere is prevented.

There is no particular restriction on the amine-based sensitizing agentand any amine-based sensitizing agent can be appropriately selecteddepending on the purpose. The amine-based sensitizing agent includes,for example, triethanol amine, triisopropanol amine, 4,4-diethylaminobenzophenone, 2-dimethylaminoethyl benzoate, 4-dimethylamino ethylbenzoate and 4-dimethylamino isoacyl benzoate.

There is no particular restriction on the content of the sensitizingagent in the overcoat composition and any content can be appropriatelyselected depending on the purpose. The content is preferably from 1% bymass to 15% by mass and more preferably from 3% by mass to 8% by mass.

-Polymerization Prohibiting Agent-

The polymerization prohibiting agent is used for increasing storagestability of the overcoat composition.

There is no particular restriction on the polymerization prohibitingagent and any polymerization prohibiting agent can be selectedappropriately depending on the purpose. The polymerization prohibitingagent includes, for example, 2,6-ditert-butyl-p-ceresol (BHT),2,3-dimethyl-6-tert-butylphenol (IA), anthraquinone, hydroquinone (HQ)and monomethyl ether hydroquinone (MEHQ).

There is no particular restriction on the content of the polymerizationprohibiting agent in the overcoat composition and any content can beappropriately selected depending on the purpose. The content ispreferably from 0.5% by mass to 3% by mass.

-Other Components-

The other components include, for example, a leveling agent, a mattingagent, waxes for adjusting film physical properties, and apolymerization inhibition-free tackifier (viscosity imparting agent)which improves the attachment property of polyolefin,polyethyleneterephthalate (PET) or the like to a recording medium.

There is no particular restriction on the viscosity of the overcoatcomposition and any viscosity can be appropriately selected depending onthe purpose. The viscosity is preferably from 30 mPa·s to 700 mPa·s at25° C. and more preferably from 200 mPa·s to 500 mPa·s. Where theviscosity is less than 30 mPa·s or in excess of 700 mPa·s, it may bedifficult to control the coating thickness of the overcoat composition.

The viscosity can be measured by using, for example, a Brookfield typeviscometer (made by Toyo Seiki Seisaku-sho, Ltd.).

The overcoat composition can be prepared as an oil-type by using asolvent. An ultraviolet light-curing type (photo-curing type) preparedby UV is preferable in terms of ensuring safety, environmentalprotection, energy saving and high productivity.

The overcoat composition is coated on a fixed image on the recordingmedium after the fixing step. For example, the overcoat composition iscoated on the recording medium immediately after formation of a fixedimage as performed in in-line coating which is carried out by oneprinting device for conducting printing and final coating, or at a lapseof short or long delay after printing as done in off-line coating inwhich printing and final coating are conducted by different printingdevices.

The coating is not necessarily given all over to the recording medium orthe fixed image, as long as the overcoat composition is coated at leaston a part of the fixed image formed on the recording medium. Theovercoat composition can be appropriately selected depending on thepurpose such as protecting the printing surface or imparting gloss.

There is no particular restriction on the coating unit and any coatingunit can be appropriately selected depending on the purpose. The coatingunit includes, for example, a liquid film coating machine such as rollcoater, flexo coater, rod coater, blade, wire bar, air knife, curtaincoater, slide coater, doctor knife, screen coater, gravure coater (forexample, offset gravure coater), slot coater, extrusion coater andinkjet coater. Coating carried out by the above-described coatersincludes, for example, forward and reverse rotating roll coating, offsetgravure, curtain coating, lithograph coating, screen coating, gravurecoating and inkjet coating.

There is no particular restriction on the average thickness of theovercoat layer and any average thickness can be appropriately selecteddepending on the purpose. The average thickness is preferably from 1 μmto 15 μm. Where the average thickness is less than 1 μm, there is a casethat repelling may take place or gloss is insufficiently imparted. Wherethe average thickness is in excess of 15 μm, there is a case that animage may be decreased in texture.

Next, where the overcoat composition is a photo-curing type overcoatcomposition, light (mainly ultraviolet light) from a light source isradiated to effect curing.

Moreover, where the overcoat composition is an oil-based overcoatcomposition, heating can be given to effect curing.

There is no particular restriction on the light source and any lightsource can be appropriately selected depending on the purpose. The lightsource includes, for example, low-pressure mercury-vapor lamp,medium-pressure mercury-vapor lamp, high-pressure mercury-vapor lamp,ultra-high pressure mercury-vapor lamp, xenon lamp, carbon arc lamp,metal halide lamp, fluorescent lamp, tungsten lamp, argon ion laser,helium cadmium laser, helium neon laser, krypton ion laser, varioustypes of semiconductor laser, YAG laser, light emitting diode, CRT lightsource, plasma light source, electron beam, γ rays, ArF excimer laser,KrF excimer laser, and F2 laser.

Here, FIG. 3 is a schematic diagram which shows one example of theovercoat layer forming unit. An overcoat layer forming unit 115 shown inFIG. 3 is provided with a coating roller 2, a metal roller 3, a pressingroller 5, a conveyance belt 6, a tray 7, a light source 8 and a scraper9.

An overcoat composition 1 is pooled between the coating roller 2 and themetal roller 3. A recording medium 4 on which a visible image has beenformed passes through a space between the coating roller 2 and thepressing roller 5, while being in contact with the coating roller 2 andthe pressing roller 5 rotating in a direction shown with arrows in thedrawing. At this time, the overcoat composition 1 on the surface of thecoating roller 2 is transferred to the recording medium 4, by which theovercoat composition 1 is coated on the recording medium 4.

The recording medium 4 on which the overcoat composition 1 has beencoated is conveyed by the conveyance belt 6 and passes below the lightsource 8. At this time, ultraviolet light is radiated from the lightsource 8 to cure the overcoat composition 1 coated on the recordingmedium 4. Thereafter, the recording medium 4 moves onto the tray 7.Moreover, the unnecessary overcoat composition 1 adhered on the pressingroller 5 is removed by the scraper 9.

The overcoat layer forming unit 115 may be formed integrally with animage forming apparatus or separated from the apparatus.

<Other Steps and Other Units>

-Charge Eliminating Step and Charge Eliminating Unit-

The charge eliminating step is a step in which charge eliminating biasis applied to the electrostatic latent image bearing member to eliminatecharge and can be favorably carried out by a charge eliminating unit.

There is no particular restriction on the charge eliminating unit. Anycharge eliminating unit can be appropriately selected from known chargeeliminating devices, as long as the charge eliminating bias can beapplied to the electrostatic latent image bearing member. The chargeeliminating unit includes, for example, a charge eliminating lamp.

-Cleaning Step and Cleaning Unit-

The cleaning step is a step of removing the toners remaining on theelectrostatic latent image bearing member and can be favorably carriedout by a cleaning unit.

There is no particular restriction on the cleaning unit. Any cleaningunit can be appropriately selected from known cleaners, as long as theelectrophotographic toner remaining on the electrostatic latent imagebearing member can be removed. The cleaning unit includes, for example,a magnetic brush cleaner, an electrostatic brush cleaner, a magneticroller cleaner, a blade cleaner, a brush cleaner, and a web cleaner.

-Recycle Step and Recycle Unit-

The recycle step is a step in which the toner which has been removed inthe cleaning step is recycled by the development unit and can befavorably carried out by the recycle unit.

There is no particular restriction on the recycle unit and any recycleunit can be used, such as known conveyance units.

-Control Step and Control Unit-

The control step is a step of controlling the individual steps describedso far and can be carried out favorably by the control unit.

There is no particular restriction on the control unit as long as it iscapable of controlling movements of the individual units. Any controlunit can be appropriately selected depending on the purpose. The controlunit includes, for example, devices such as a sequencer and a computer.

Here, FIG. 4 is a schematic diagram which shows an example of the colorimage forming apparatus of the present invention. An image formingapparatus 100A given in FIG. 4 is provided with a photosensitive drum10, the charging roller 20 as a charging unit, an exposure device (notillustrated) as an exposure unit, developing devices as developmentunits (black developing device 45K, yellow developing device 45Y,magenta developing device 45M and cyan developing device 45C), anintermediate transfer member 50, a cleaner 60 having a cleaning blade asa cleaning unit and a charge eliminating lamp 70 as a charge eliminatingunit.

The intermediate transfer member 50 is an endless belt which is laidacross by three rollers 51 installed internally and able to move in adirection indicated by an arrow. A portion of the three rollers 51 alsoacts as a transfer bias roller capable of applying a predeterminedtransfer bias (primary transfer bias) to the intermediate transfermember 50.

Further, the cleaner 90 having the cleaning blade is disposed in thevicinity of the intermediate transfer member 50. Moreover, a transferroller 80 as a transfer unit capable of applying transfer bias fortransferring a toner image (secondary transfer) on a recording medium 95is disposed so as to oppose the intermediate transfer member 50.

Still further, a corona electrifier 52 for imparting electric charges toa toner image on the intermediate transfer member 50 is disposed betweena part of the intermediate transfer member 50 in contact with thephotosensitive drum 10 and a part of the recording medium 95 in contactwith the intermediate transfer member 50 around the intermediatetransfer member 50.

The developing devices of black color (K), yellow color (Y), magentacolor (M) and cyan color (C) (black developing device 45K, yellowdeveloping device 45Y, magenta developing device 45M, cyan developingdevice 45C) are respectively provided with developer containers (42K,42Y, 42M, 42C), developer supplying rollers (43K, 43Y, 43M, 43C) anddeveloping rollers (44K, 44Y, 44M, 44C).

In the image forming apparatus 100A, the charging roller 20 is used touniformly charge the photosensitive drum 10 and, thereafter, an exposuredevice (not illustrated) is used to expose exposure light 30 imagewiseon the photosensitive drum 10, thereby forming an electrostatic latentimage. Next, the electrostatic latent image formed on the photosensitivedrum 10 is developed by supplying developers from the developing devices(black developing device 45K, yellow developing device 45Y, magentadeveloping device 45M, cyan developing device 45C) to form a toner imageand, thereafter, the toner image is transferred on the intermediatetransfer member 50 (primary transfer) by transfer bias applied from theroller 51. Further, the toner image on the intermediate transfer member50 is given electric charges by the corona electrifier 52 and,thereafter, transferred on the recording medium 95 (secondary transfer).Toners remaining on the photosensitive drum 10 are removed by thecleaner 60, and the photosensitive drum 10 is temporarily subjected tocharge elimination by the charge eliminating lamp 70.

Moreover, in the image forming apparatus 100A, an overcoat layer formingunit (not illustrated) can be placed at any given location after thetoner image is fixed.

FIG. 5 is a schematic diagram which shows another example of the colorimage forming apparatus of the present invention. An image formingapparatus 100B is a tandem-type color image forming apparatus andprovided with a copier main body 150, a sheet feeding table 200, ascanner 300 and an automatic document feeder (ADF) 400.

The copier main body 150 is provided with an endless-belt likeintermediate transfer member 50 at the center part thereof. Theintermediate transfer member 50 is laid across by supporting rollers 14,15, 16 and able to rotate in a direction indicated by an arrow.

A cleaner 17 for removing toners remaining on the intermediate transfermember 50 is disposed in the vicinity of the supporting roller 15.Further, a tandem-type developing device 120 on which four image formingunits 18 of yellow, cyan, magenta and black are installed in parallel soas to be opposed is disposed on the intermediate transfer member 50 laidacross by the supporting roller 14 and the supporting roller 15 in aconveyance direction thereof.

As shown in FIG. 6, each of the image forming units 18 of these colorsis provided with the photosensitive drum 10, the charging roller 20 foruniformly charging the photosensitive drum 10, a developing device 61for developing the electrostatic latent image formed on thephotosensitive drum 10 with each of the developers of black (K), yellow(Y), magenta (M) and cyan (C) to form a toner image, a transfer roller62 for transferring the color toner images of each color on theintermediate transfer member 50, a cleaner 63 and a charge eliminatinglamp 64.

Further, an exposure device 21 is disposed in the vicinity of thetandem-type developing device 120. The exposure device 21 exposesexposure light L on the photosensitive drums 10 (black photoconductor10K, yellow photoconductor 10Y, magenta photoconductor 10M and cyanphotoconductor 10C) to form an electrostatic latent image.

Still further, a secondary transfer device 22 is disposed on theopposite side to the side where the tandem-type developing device 120 ofthe intermediate transfer member 50 is disposed. The secondary transferdevice 22 is formed of a secondary transfer belt 24 which is an endlessbelt laid across by a pair of rollers 23 and configured in such a mannerthat recording paper conveyed on the secondary transfer belt 24 and theintermediate transfer member 50 are allowed to be in contact with eachother.

A fixing apparatus 25 is disposed in the vicinity of the secondarytransfer device 22. The fixing apparatus 25 is provided with a fixingbelt 26 which is an endless belt and a pressure roller 27 which isdisposed so as to be pressed by the fixing belt 26.

In addition, a sheet reversing device 28 for reversing recording paperto form an image on both sides of the recording paper is disposed in thevicinity of the secondary transfer device 22 and the fixing apparatus25.

Next, a description will be given of a full color image formation (colorcopy) by using the image forming apparatus 100B.

First, documents are set on a document counter 130 of the automaticdocument feeder (ADF) 400 or the automatic document feeder 400 is openedto set documents on a contact glass 32 of the scanner 300, then, theautomatic document feeder 400 is closed. Next, depression of a startswitch (not illustrated) will actuate the scanner 300 after documentsare conveyed and moved to the contact glass 32 when the documents areset on the automatic document feeder 400, whereas actuating the scanner300 immediately when the documents are set on the contact glass 32,thereby allowing a first traveling body 33 and a second traveling body34 to travel. At this time, light from a light source is radiated fromthe first traveling body 33, and also light reflected from the surfaceof the documents is reflected on a mirror of the second traveling body34 and received by a reading sensor 36 through an imaging lens 35.Thereby, color documents (color images) are read to give imageinformation of each color, that is, black, yellow, magenta and cyan.

Further, after an electrostatic latent image of each color is formed onthe photosensitive drum 10 on the basis of image information of eachcolor obtained by the exposure device 21, the electrostatic latent imageof each color is developed by a developer supplied from the developingdevices 61 for the respective colors to form a toner image of eachcolor. The thus formed toner image of each color is sequentiallylaminated on the intermediate transfer member 50 which movesrotationally by the supporting rollers 14, 15 and 16, and transferred(primary transfer) to form a composite toner image on the intermediatetransfer member 50.

In the sheet feeding table 200, one of the sheet feeding rollers 142 isselectively rotated to deliver recording paper from one of the sheetfeeding cassettes 144 provided in a multistage manner on a paper bank143. The thus delivered recording paper is separated one by one by aseparation roller 145 and sent to a sheet feeding path 146, then, therecording paper is conveyed by a conveyance roller 147 and guided into aheat feeding path 148 inside a copier main body 150 and stopped byhitting the recording paper against a resist roller 49. Alternatively,recording paper on a manual tray 151 is delivered, separated one by oneby a separation roller 58, placed in a manual sheet feeding path 53 andstopped by hitting the recording paper against the resist roller 49. Itis noted that the resist roller 49 is in general grounded before use,but in this case the roller 49 may be used, with bias being applied, toremove dust on the recording paper.

Then, the resist roller 49 is rotated in synchronization with acomposite toner image formed on the intermediate transfer member 50, bywhich the recording paper is sent between the intermediate transfermember 50 and the secondary transfer device 22. The composite tonerimage is transferred (second transfer) on the recording paper.

The recording paper on which the composite toner image has beentransferred is conveyed by the secondary transfer device 22 and sent toa fixing apparatus 25. Then, the composite toner image is heated andpressed on the fixing apparatus 25 by the fixing belt 26 and thepressure roller 27 and fixed on the recording paper. Thereafter, therecording paper is changed over by a change-over pawl 55 and dischargedby a discharge roller 56 and stacked on a discharge tray 57.Alternatively, the recording paper is changed over by the change-overpawl 55, reversed by the sheet reversing device 28 and again guided intoa transfer position to form an image on the back face as well.Thereafter, the paper is discharged by the discharge roller 56 andstacked on the discharge tray 57.

It is noted that toners remaining on the intermediate transfer member 50after transfer of the composite toner image are removed by the cleaner17.

In the image forming apparatus 100B, an overcoat layer forming unit (notillustrated) can be placed at any given place, after the toner image isfixed.

According to the color image forming method and the color image formingapparatus of the present invention, it is possible to effectively form ahigh-grade and beautiful image which is great in durability even information of a color image which is greater in content of a releasingagent and lower in attachment property to an overcoat layer than ablack-and-white image.

EXAMPLES

Hereinafter, a detailed description will be given of the presentinvention with reference to examples, to which the present inventionshall not be, however, limited in any way.

In the following examples and comparative examples, the resin wasmeasured for its weight-average molecular weight and glass transitiontemperature and the wax was measured for its isoparaffin content andweight-average molecular weight by the following methods.

<<Weight-Average Molecular Weight>>

The weight-average molecular weight of the resin was measured by a gelpermeation chromatography (GPC). A column was stabilized in a heatchamber kept at 40° C. Tetrahydrofuran (THF) as a solvent was fed at aflow rate of 1mL/minute to the column stabilized at this temperature,thereby preparing a THF sample solution of the resin, the sampleconcentration of which was adjusted from 0.05% by mass to 0.6% by mass.The weight-average molecular weight was measured by feeding the thusprepared THF sample solution at a quantity of 50 μL to 200 μL.

On measurement of the molecular weight of the sample, the sample wascalculated for its molecular weight distribution with reference to arelationship between logarithmic values and number of counts of astandard curve prepared by several types of monodisperse polystyrenestandard samples. The polystyrene standard samples for preparing thestandard curve include those having the following molecular weights,6×10², 2.1×10², 4×10³, 1.75×10⁴, 5.1×10⁴, 1.1×10⁵, 3.9×10⁵, 8.6×10⁵,2×10⁶, 4.48×16⁶ (made by Pressure Chemical Co. or Tosoh Corporation). Itis appropriate to use at least 10 polystyrene standard samples. Further,an RI (refraction index) detector was used as a detector.

<<Glass Transition Temperature>>

The glass transition temperature of the resin was measured withreference to a DSC curve obtained by means of a differential scanningcalorimetry (DSC). TA-60W and DSC-60 (made by Shimadzu Corporation) wereused to obtain the DSC curve and the glass transition temperature wasmeasured under the following conditions.

[Measurement Conditions]

-   -   Sample container: aluminum-made sample pan (with lid)    -   Sample quantity: 5 mg    -   Reference: aluminum-made sample pan (alumina 10 mg)    -   Atmosphere: nitrogen (flow rate: 50 mL/minute)    -   Temperature conditions        -   Temperature at the start: 20° C.        -   Temperature elevation speed: 10° C./minute        -   Temperature at the end: 150° C.        -   Retention time: none        -   Temperature lowering speed: 10° C./minute        -   Temperature at the end: 20° C.        -   Retention time: none        -   Temperature elevation speed: 10° C./minute        -   Temperature at the end: 150° C.

The above measurement results were analyzed with reference to the dataanalysis software TA-60 version 1.52 (made by Shimadzu Corporation).

In analysis of the measurement results, a range of ±5° C. was specifiedon the basis of a maximum peak found on a DSC differential curve of asecond temperature elevation which is a DrDSC curve, and peak analysisfunctions of the data analysis software were used to determine a peaktemperature. Next, in a range of the peak temperature of the DSC curvefrom +5° C. to −5° C., the peak analysis functions of the data analysissoftware were used to determine a maximum endothermic temperature of theDSC curve. This temperature corresponds to a melting point.

At an endothermic peak of a main peak in a range from 40° C. to 100° C.obtained during the temperature elevation, an intersecting point betweena line formed by middle points of a baseline before and after theendothermic peak and a differential calorimetry curve was given as aglass transition temperature (Tg).

<<Isoparaffin Content in Wax and Weight-Average Molecular Weight ofWax>>

The isoparaffin content (% by mass) in the wax and the weight-averagemolecular weight of the wax were measured by using JMS-T100GC “AccuTOFGC” (made by JEOL Ltd.) as a gas chromatograph TOF-type massspectrometer according to a FD (field desorption) method.

Example 1

<Preparation of Toner 1>

[Formulation]

-   -   Polyester resin (weight-average molecular weight Mw: 68,500,        glass transition temperature Tg: 65.9° C.) . . . 89.5 parts by        mass    -   Microcrystalline wax (isoparaffin content: 15% by mass,        weight-average molecular weight Mw: 645) . . . 5 parts by mass    -   Carbon black (#44, made by Mitsubishi Kasei Corp.) . . . 5 parts        by mass    -   Charge control agent (Spiron black TR-H made by Hodogaya        Chemical Co., Ltd.) . . . 1 part by mass

After the above-described formulation was mixed and kneaded at 120° C.by using a biaxial extruder (BCTA-type, made by Buehler GmbH), it waspulverized and classified to give a weight average particle diameter of11.0 μm by using an air-flow pulverizer (jet mill, made by NisshinEngineering Inc.). Then, the formulation was mixed with 2.2% by mass ofsilica (R-972, made by Nippon Aerosil Co., Ltd.) by using a Henschelmixer (FM-type, made by Nippon Coke & Engineering Co., Ltd.) to prepareblack toner 1.

Yellow toner 1 was prepared in the same manner as in the black toner 1except that C.I. Pigment Yellow 17 was used in place of the carbon blackin production of the black toner 1.

Magenta toner 1 was prepared in the same manner as in the black toner 1except that C. I. Pigment Red 57 was used in place of the carbon blackin production of the black toner 1.

Cyan toner 1 was prepared in the same manner as in the black toner 1except that C.I. Pigment Blue 15 was used in place of the carbon blackin production of the black toner 1.

The thus obtained black, yellow, magenta and cyan toners 1 were measuredfor an average circularity and volume average particle diameter Dv bythe following procedures, and the average circularity was 0.90 andvolume average particle diameter Dv was 8.0 μm.

<Average Circularity>

The average circularity of toners was measured by using a flow-typeparticle image analyzer (“FPIA-2100” made by Sysmex Corporation) andanalysis was made by using the analysis software (FPIA-2100 DataProcessing Program for FPIA Version 00-10). More specifically, 10% bymass of a surfactant (alkylbenzene sulfonate, Neogen SC-A, made byDai-Ichi Kogyo Seiyaku Co., Ltd.) was added into a glass beaker (100 mL)at a quantity of 0.1 mL to 0.5 mL and each of the toners was added at aquantity of 0.1 g to 0.5 g. Then, the resultant was mixed by using amicrospatula and ion exchanged water was then added thereto at aquantity of 80 mL. The thus obtained dispersion solution was dispersedfor three minutes by using an ultrasonic homogenizer (made by HondaElectronics Co., Ltd.). The FPIA-2100 was used to measure theconfiguration and distribution of each toner until the dispersionsolution gave concentrations of 5,000 particles/μL to 15,000particles/μL.

In the above measurement, it is important that dispersion solution givesconcentrations of 5,000 particles/μL to 15,000 particles/μL in order tomeasure the average circularity at a high reproducibility.

<Volume Average Particle Diameter Dv of Toners>

Regarding a volume average particle diameter (Dv) of toners, a CoulterMultisizer III type measuring device (made by Beckman Coulter Inc.) wasconnected to a PC-9801 personal computer (made by NEC Corporation) viaan interface (made by The Institute of JUSE) for outputting the numberdistribution and volume distribution, by which the particle sizedistribution was measured.

More specifically, a surfactant (alkyl benzene sulfonate) was added at aquantity of 0.1 mL to 5 mL as a dispersing agent to 100 mL to 150 mL ofan electrolyte solution. It is noted that the electrolyte solution wasobtained by preparing 1% by mass of an aqueous solution by using primarysodium chloride. ISOTON-II (made by Beckman Coulter Inc.) was used.

Then, a sample was added at a quantity of 2 mg to 20 mg to causesuspension and, thereafter, a resultant was dispersed for 1 minute to 3minutes by using an ultrasonic homogenizer. The volume and number oftoners were measured from the thus obtained dispersion solution througha 100-μm aperture to calculate the volume distribution and numberdistribution.

The following 13 channels were used, that is, 2.00 μm or more but lessthan 2.52 μm; 2.52 μm or more but less than 3.17 μm; 3.17 μm or more butless than 4.00 μm; 4.00 μm or more but less than 5.04 μm; 5.04 μm ormore but less than 6.35 μm; 6.35 μm or more but less than 8.00 μm; 8.00μm or more but less than 10.08 μm; 10.08 μm or more but less than 12.70μm; 12.70 μm or more but less than 16.00 μm; 16.00 μm or more but lessthan 20.20 μm; 20.20 μm or more but less than 25.40 μm; 25.40 μm or morebut less than 32.00 μm; 32.00 μm or more but less than 40.30 μm.Particles with the particle diameter of 2.00 μm or more to less than40.30 μm were to be measured.

<Preparation of Developers 1>

A carrier prepared by coating a silicone resin on magnetite particleswith a volume average particle diameter of 50 μm so as to give anaverage thickness of 0.5 μm was used to mix the toners 1 for therespective colors so as to give a toner concentration of 5.0% by mass,thereby preparing each of the black, yellow, magenta and cyan developers1.

<Formulation of Overcoat Composition 1>

9 parts by mass of pentaerythritol tetraacrylate as a polymerizableunsaturated compound, 2.5 parts by mass of ethoxydiethylene glycolacrylate as a polymerizable unsaturated compound, 30 parts by mass oftrimethylolpropane triacrylate as a polymerizable unsaturated compoundand 0.3 parts by mass of hydroquinone as a polymerization prohibitingagent were put into a beaker and heated up to 120° C. while agitating,and 50 parts by mass of a diallylphthalate prepolymer (Daiso Dap 100,made by Daiso Co., Ltd.) was dissolved therein. Further, a substanceprepared by dissolving 2 parts by mass of aluminum isopropylate in 2parts by mass of toluene was gradually added and agitated for 20 minutesat 110° C. During this time, toluene added as a solvent was removed froma system. Thereby, a photo-curing varnish agent was obtained.

Next, 75 parts by mass of the photo-curing varnish base agent, 60 partsby mass of 1,6-hexanediol diacrylate as a polymerizable unsaturatedcompound, 10 parts by mass of benzophenone as a photo-polymerizationinitiator, 5 parts by mass of p-dimethylamino acetophenone, and 10 partsby mass of phenylglycol monoacrylate as a viscosity adjusting agent weremixed and well kneaded by using a three roll mill. Thus, obtained was aphoto-curing overcoat composition 1.

The thus obtained overcoat composition 1 was measured for viscosity bythe following procedures, which was 200 mPa·s.

<Measurement of Viscosity>

The viscosity of the overcoat composition was measured at 25° C. byusing a Brookfield type viscometer (made by Toyo Seiki Seisaku-sho,Ltd.).

<Fusion (Color Difference ΔE*) Test>

A color image forming apparatus (IMAGIO MP C7500, made by Ricoh CompanyLtd.) was used to form a red-color fixed solid image prepared byoverlapping two color toners of magenta and yellow (wax content of 10%by mass, toner adhesion quantity of 0.8 mg/cm²) on an OHP sheet (for PPC(plain paper opier), A4-size sheet, without cut 27054, made by A-OneCo., Ltd.). The OHP sheet on which the red-color fixed solid image wasformed was sandwiched with another OHP sheet and a spectroscopicdensitometer (X-Rite 938, made by X-Rite Incorporated) was used tomeasure lightness L1, chromaticity a1 and chromaticity b1 of the imageaccording to the L*a*b* color system (before titration). The OHP sheetwas sandwiched with another OHP sheet in order to keep the spectroscopicdensitometer (X-Rite 938, made by X-Rite Incorporated) clean.

Next, a fusion tester shown in FIG. 7 was used to put an overcoatcomposition 114 into a dropping burette 113 so as to be 10 mm in heightabove the red-color fixed solid image formed on the OHP sheet 112 whichwas placed on a titration base 111. Next, the overcoat composition 114was dropped at a quantity of 0.4 mg and the overcoat composition 114 wasremoved by using a microwipe MU-2000 (made by MCC Co., Ltd.) after 10seconds passed. The OHP sheet on which the red-color fixed solid imagewas formed was sandwiched with another OHP sheet and the spectroscopicdensitometer (X-Rite 938, made by X-Rite Incorporated) was used tomeasure lightness L2, chromaticity a2 and chromaticity b2 of the imageaccording to the L*a*b* color system (after titration). These measuredvalues were applied to the following formula (1) to calculate a colordifference ΔE* before and after titration of the overcoat composition.ΔE*=[(a2−a1)²+(b2−b1)²+(L2−L1)²]^(1/2)  (1)<Preparation of Printed Matter>

A color image forming apparatus equipped with the developers 1 for therespective colors (IMAGIO MP C7500, made by Ricoh Company Ltd.) was usedto output a test chart No. 4 according to ISO/IEC 15775:1999 on PODgloss coated paper made by Oji Paper Co., Ltd. (basis weight: 128 g/m²)as a recording medium under conditions that toner was adhered in aquantity of 0.4 mg/cm² on a solid image part of single color toner.Thereby, a printed matter was obtained.

<Measurement of Wax Coverage Factor>

Red, green and blue fixed solid images formed with at least two tonersusing a test chart No. 4 according to ISO/IEC 15775:1999 were cut outand exposed for 5 minutes to saturated vapor of 5% by mass of an aqueousruthenium tetroxide solution (made by TABB Inc.), by which rutheniumtetroxide was chemically modified.

Then, the surface of an image on the chemically-modified printed matterwas observed by using a transmission electron microscope/scanningelectron microscope (ULTRA55 made by Carl Zeiss AG) with magnificationsof 1,000 at an accelerating voltage of 0.8 kV to obtain a reflectionelectron SEM image.

Image processing was carried out in which Photoshop (made by AdobeSystems Inc.) was used to classify pixels comprising the obtainedreflection electron SEM image into a black part and a white part(binarization), thereby obtaining a binarization image. Then,measurement was made for an area percentage of the black part withrespect to an entire area of the binarization image (wax coveragefactor). The results are shown in Table 2. The red, green and blue fixedsolid images were measured to obtain the wax coverage factors of therespective colors, of which a maximum value is shown.

<Evaluation of Repelling Property (Wettability)>

A UV varnish coater (SG610V, made by Shinano Kenshi Co., Ltd.) was usedto coat the overcoat composition 1 on the printing surface of theto-be-printed matter at a coater speed of 10 m/minute at radiation of120 W/cm so as to give a thickness of 5 g/m² (4.5 μm). The photo-curingovercoat composition 1 was cured by using the UV varnish coater. Aftercuring, the overcoat composition 1 on the printed matter wasmacroscopically checked for the extent of repelling and evaluated on thebasis of the following criteria. The results are shown in Table 2. Whererepelling is found on the overcoat composition, developed is aseveral-millimeter to several-centimeter region substantially devoid ofthe overcoat layer. This region reflects light unnaturally, which isfound to be an unfavorable image just by sight.

[Criteria]

A: No repelling

B: Repelling is found very slightly but acceptable

C: Repelling is found to some extent but acceptable

D: Apparent repelling is found

<Evaluation of Attachment Property>

A UV varnish coater (SG610V, made by Shinano Kenshi Co., Ltd.) was usedto coat the overcoat composition 1 on the printing surface of theto-be-printed matter so as to give a thickness of 5 g/m² (4.5 μm) and UVwas radiated by using the UV varnish coater to cure the overcoatcomposition.

The overcoat layer on the printed matter after curing was cut by usingan utility knife so as to give a board made up of 100 cells at 1 mmintervals according to JIS K5400. Then, an adhesive cellophane adhesivetape (CT-18, made by Nichiban Co., Ltd.) was attached on the surface ofthe printed matter and peeled off. And, the number of cells which werenot peeled off was counted by using a magnifying glass and evaluationwas made on the basis of the following criteria. The results are shownin Table 2.

[Criteria]

A: 100/100

B: 80/100 to 99/100

C: 40/100 to 79/100

D: 0/100 to 39/100

<State of Image>

An image after formation of the overcoat layer was checkedmacroscopically for the presence or absence of distortion with referenceto the image before formation of the overcoat layer. The state of theimage was evaluated on the basis of the following criteria.

[Criteria]

A: Image is free of distortion and favorable.

B: Image is slightly distorted.

C: Image is greatly distorted.

Example 2

<Preparation of Toners 2>

Black, yellow, magenta and cyan toners 2 were prepared in the samemanner as in Example 1 except that the microcrystalline wax used inExample 1 was changed to a mixture of microcrystalline wax with paraffinwax (isoparaffin content: 9% by mass, weight-average molecular weightMw: 520).

The thus obtained toners 2 for the respective colors were measured foraverage circularity and volume average particle diameter Dv in the samemanner as in Example 1, and the circularity was 0.91 and volume averageparticle diameter Dv was 6.8 μm.

<Preparation of Developers 2>

A carrier prepared by coating a silicone resin on magnetite particleswith a volume average particle diameter of 50 μm so as to give anaverage thickness of 0.5 μm was used to mix the toners 2 for therespective colors so as to give a toner concentration of 5.0% by mass,thereby preparing the developers 2 for the respective colors.

<Formulation of Overcoat Composition 2>

40 parts by mass of a polyester acrylate oligomer (EBECRYL846,weight-average molecular weight Mw: 1,100, made by Daicel Cytec CompanyLtd.), 2.5 parts by mass of ethoxydiethylene glycol acrylate as apolymerizable unsaturated compound, 30 parts by mass of tripropyleneglycol diacrylate as a polymerizable unsaturated compound, 50 parts bymass of acryloylmorpholine as a polymerizable unsaturated compound, 0.2parts by mass of hydroquinone monomethyl ether as a polymerizationprohibiting agent, 8 parts by mass of benzoin ethyl ether as aphoto-polymerization initiator and 3 parts by mass of triisopropanolamine as a sensitizing agent were mixed and agitated at 60° C. for 20minutes to prepare a photo-curing overcoat composition 2.

The thus obtained overcoat composition 2 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 460mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that thedevelopers 1 and the overcoat composition 1 used in Example 1 werechanged to the developers 2 and overcoat composition 2. The results areshown in Table 2.

Example 3

<Preparation of Toners 3>

Black, yellow, magenta and cyan toners 3 were prepared in the samemanner as in Example 1 except that microcrystalline wax used in Example1 was changed to a mixture of microcrystalline wax with paraffin wax(isoparaffin content: 4.1% by mass, weight-average molecular weight Mw:550).

The thus obtained toners 3 for the respective colors were measured foraverage circularity and volume average particle diameter Dv in the samemanner as in Example 1, and the average circularity was 0.91 and volumeaverage particle diameter Dv was 7.9 μm.

<Preparation of Developers 3>

A carrier prepared by coating a silicone resin on magnetite particleswith a volume average particle diameter of 50 μm so as to give anaverage thickness of 0.5 μm was used to mix the toners 3 for therespective colors so as to give a toner concentration of 5.0% by mass,thereby preparing the developers 3 for the respective colors.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that thedevelopers 1 and the overcoat composition 1 used in Example 1 werechanged to the developers 3 and overcoat composition 2. The results areshown in Table 2.

Example 4

<Preparation of Toners 4>

Black, yellow, magenta and cyan toners 4 were prepared in the samemanner as in Example 1 except that the microcrystalline wax used so inExample 1 was changed to paraffin wax (weight-average molecular weightMw: 500).

The thus obtained toners 4 for the respective colors were measured foraverage circularity and volume average particle diameter Dv in the samemanner as in Example 1, and the average circularity was 0.89 and DV was8.0 μm.

<Preparation of Developers 4>

A carrier prepared by coating a silicone resin on magnetite particleswith a volume average particle diameter of 50 μm so as to give anaverage thickness of 0.5 μm was used to mix the toners 4 for therespective colors so as to give a toner concentration of 5.0% by mass,thereby preparing the developers 4 for the respective colors.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that thedevelopers 1 and the overcoat composition 1 used in Example 1 werechanged to the developers 4 and overcoat composition 2. The results areshown in Table 2.

Example 5

<Preparation of Toners 5>

Black, yellow, magenta and cyan toners 5 were prepared in the samemanner as in Example 1 except that 5 parts by mass of themicrocrystalline wax used in Example 1 was changed to 1.6 parts by massof paraffin wax (weight-average molecular weight Mw: 500).

The thus obtained toners 5 for the respective colors were measured foraverage circularity and volume average particle diameter Dv in the samemanner as in Example 1, and the average circularity was 0.90 and volumeaverage particle diameter Dv was 7.8 μm.

<Preparation of Developers 5>

A carrier prepared by coating a silicone resin on magnetite particleswith a volume average particle diameter of 50 μm so as to give anaverage thickness of 0.5 μm was used to mix the color toners 5 for therespective colors so as to give a toner concentration of 5.0% by mass,thereby preparing the developers 5 for the respective colors.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that thedevelopers 1 and the overcoat composition 1 used in Example 1 werechanged to the developers 5 and overcoat composition 2. The results areshown in Table 2.

Example 6

<Preparation of Toners 6>

Black, yellow, magenta and cyan toners 6 were prepared in the samemanner as in Example 1 except that the microcrystalline wax used inExample 1 was changed to a mixture of microcrystalline wax with paraffinwax (isoparaffin content: 11.3% by mass, weight average so molecularweight Mw: 480).

The thus obtained toners 6 for the respective colors were measured foraverage circularity and volume average particle diameter Dv in the samemanner as in Example 1, and the average circularity was 0.91 and volumeaverage particle diameter Dv was 7.8 μm.

<Preparation of Developers 6>

A carrier prepared by coating a silicone resin on magnetite particleswith a volume average particle diameter of 50 μm so as to give anaverage thickness of 0.5 μm was used to mix the toners 6 for therespective colors so as to give a toner concentration of 5.0% by mass,thereby preparing the developers 6 for the respective colors.

<Preparation of Overcoat Composition 3>

10 parts by mass of an urethane acrylate oligomer (EBECRYL5129,weight-average molecular weight Mw: 800, made by Daicel Cytec CompanyLtd.), 41 parts by mass of 1,6-hexanediol diacrylate as a polymerizableunsaturated compound, 10 parts by mass of cyclohexyl acrylate as apolymerizable unsaturated compound, 80 parts by mass of ethylcarbitolacrylate as a polymerizable unsaturated compound, 2.5 parts by mass ofethoxydiethylene glycol acrylate as a polymerizable unsaturatedcompound, 0.3 parts by mass of hydroquinone monomethyl ether as apolymerization prohibiting agent and 6 parts by mass of benzyl(1,2-diphenyl ethanedione) as a photo-polymerization initiator weremixed and agitated at 60° C. for 20 minutes to obtain a photo-curingovercoat composition 3.

The thus obtained overcoat composition 3 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 20mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that thedevelopers 1 and the overcoat composition 1 used in Example 1 werechanged to the developers 6 and overcoat composition 3. The results areshown in Table 2.

Example 7

<Preparation of Overcoat Composition 4>

60 parts by mass of a polyester acrylate oligomer (EBECRYL1830,weight-average molecular weight Mw: 1,500, made by Daicel Cytec CompanyLtd.), 30 parts by mass of bisphenol A ethylene oxide adduct diacrylate(V#700, made by Osaka Organic Chemical Industry Ltd.) as a polymerizableunsaturated compound, 5 parts by mass of 2-ethylhexyl acrylate as apolymerizable unsaturated compound, 20 parts by mass of 1,6-hexanedioldiacrylate as a polymerizable unsaturated compound, 2.5 parts by mass ofethoxydiethylene glycol acrylate as a polymerizable unsaturatedcompound, 0.4 parts by mass of 2,6-ditert-butyl-p-cresol (BHT) as apolymerization prohibiting agent and 9 parts by mass of Irgacure 184(made by Ciba Specialty Chemicals Inc.) as a photo-polymerizationinitiator were mixed and agitated at 60° C. for 20 minutes to obtain aphoto-curing overcoat composition 4.

The thus obtained overcoat composition 4 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 740mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that theovercoat composition 1 used in Example 1 was changed to the overcoatcomposition 4. The results are shown in Table 2.

Example 8

<Preparation of Overcoat Composition 5>

9 parts by mass of pentaerythritol tetraacrylate as a polymerizableunsaturated compound, 2.5 parts by mass of ethoxydiethylene glycolacrylate as a polymerizable unsaturated compound, 30 parts by mass oftrimethylolpropane triacrylate as a polymerizable unsaturated compoundand 0.3 parts by mass of hydroquinone as a polymerization prohibitingagent were put into a beaker and heated up to 120° C. while agitating,and 50 parts by mass of a diallylphthalate prepolymer (Daiso Dap 100,made by Daiso Co., Ltd.) was also dissolved. Further, 2 parts by mass ofaluminum isopropylate was dispersed in 2 parts by mass of toluene, aresultant thereof was gradually added and agitated at 110° C. for 20minutes. During this time, toluene added as a solvent was removed from asystem o obtain a photo-curing varnish base agent.

Next, 70 parts by mass of the photo-curing varnish base agent, 60 partsby mass of 1,6-hexanediol diacrylate as a polymerizable unsaturatedcompound, 10 parts by mass of benzophenone as a photo-polymerizationinitiator, 5 parts by mass of p-dimethylamino acetophenone, 10 parts bymass of phenylglycol monoacrylate as a viscosity adjusting agent, and4.5 parts by mass of polyoxyethyleneglycol alkylether as a surfactantwere mixed and well kneaded by using a three roll mill to obtain aphoto-curing overcoat composition 5.

The thus obtained overcoat composition 5 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 180mPa·s.

<Evaluation>

Evaluation was made in the same manner as n Example 1 except that theovercoat composition 1 used in Example 1 was changed to the overcoatcomposition 5. The results are shown in Table 2.

Example 9

<Preparation of Overcoat Composition 6>

60 parts by mass of a polyester acrylate oligomer (EBECRYL1830,weight-average molecular weight Mw: 1,500, made by Daicel Cytec CompanyLtd.), 30 parts by mass of bisphenol A ethylene oxide adduct diacrylate(V#700, made by Osaka Organic Chemical Industry Ltd.) as a polymerizableunsaturated compound, 3 parts by mass of 2-ethylhexyl acrylate as apolymerizable unsaturated compound, 20 parts by mass of 1,6-hexanedioldiacrylate as a polymerizable unsaturated compound, 2.5 parts by mass ofethoxydiethylene glycolacrylate as a polymerizable unsaturated compound,0.4 parts by mass of 2,6-ditert-butyl-p-cresol (BHT) as a polymerizationprohibiting agent, 9 parts by mass of Irgacure 184 (made by CibaSpecialty Chemicals Inc.) as a photo-polymerization initiator and 2parts by mass of sodium dialkylsulfosuccinate as an anionic surfactantwere mixed and agitated at 60° C. for 20 minutes to obtain aphoto-curing overcoat composition 6.

The thus obtained overcoat composition 6 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 410mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that theovercoat composition 1 used in Example 1 was changed to the overcoatcomposition 6. The results are shown in Table 2.

Example 10

<Preparation of Toners 7)

-Synthesis of Unmodified Polyester (Low Molecular Weight Polyester)-

67 parts by mass of bisphenol A ethylene oxide 2-mole adduct, 84 soparts by mass of bisphenol A propion oxide 3-mole adduct, 274 parts bymass of terephthalic acid, and 2 parts by mass of dibutyltin oxide wereplaced into a reaction tank equipped with a cooling tube, an agitatorand a nitrogen introducing tube and allowed to react under normalpressure at 230° C. for 8 hours.

Next, the thus obtained reaction solution was allowed to react for 6hours under reduced pressure of 10 mmHg to 15 mmHg, thereby synthesizingan unmodified polyester.

The thus obtained unmodified polyester was 2,200 in number averagemolecular weight (Mn), 5,700 in weight-average molecular weight Mw and56° C. in glass transition temperature Tg.

-Formulation of Master Batch (MB)-

1,000 parts by mass of water, 540 parts by mass of carbon black (Printex35, made by Evonik Degussa Japan Ltd., DBP oil absorption=42 mL/100 g,pH=9.5) and 1,200 parts by mass of the unmodified polyester were mixedby using a Henschel mixer (made by Nippon Coke & Engineering Co., Ltd.).

After the thus obtained mixture was kneaded at 150° C. for 30 minutes byusing a two-roll mill, the resultant was rolled and cooled, and then,pulverized by using a pulverizer (made by Hosokawa Micron Corporation)to prepare a master batch.

-Synthesis of Prepolymer-

682 parts by mass of bisphenol A ethyleneoxide 2-mole adduct, 81 partsby mass of bisphenol A propylene oxide 2-mole adduct, 283 parts by massof terephthalic acid, 22 parts by mass of trimellitic anhydride, and 2parts by mass of dibutyltin oxide were placed into a reaction vesselequipped with a cooling tube, an agitator and a nitrogen introducingtube and allowed to react under normal pressure at 230° C. for 8 hours.

Next, the thus obtained reaction solution was allowed to react for 5hours under reduced pressure of 10 mmHg to 15 mmHg, thereby synthesizingan intermediate polyester.

The thus obtained intermediate polyester was 2,100 in number averagemolecular weight Mn, 9,600 in weight-average molecular weight Mw, 55° C.in glass transition temperature Tg, 0.5 mg KOH/g in acid value and 49 mgKOH/g in hydroxyl value.

Then, 411 parts by mass of the intermediate polyester, 89 parts by massof isophorone diisocyanate and 500 parts by mass of ethyl acetate wereplaced into a reaction vessel equipped with a cooling tube, an agitatorand a nitrogen introducing tube and allowed to react at 100° C. for 5hours, thereby synthesizing a prepolymer (modified polyester capable ofreacting with an active hydrogen group-containing compound).

The thus obtained prepolymer was 1.60% by mass in content of freeisocyanate and the prepolymer was 50% by mass in solid-basedconcentration (after being allowed to stand at 150° C. for 45 minutes).

-Synthesis of Ketimine (Active Hydrogen Group-Containing Compound)-

30 parts by mass of isophorone diamine and 70 parts by mass ofmethylethyl ketone were placed into a reaction vessel at which astirring rod and a thermometer were set, and allowed to react at 50° C.for 5 hours, thereby synthesizing a ketimine compound (active hydrogengroup-containing compound).

The thus obtained ketimine compound (active hydrogen group-containingcompound) was 423 in amine value.

-Synthesis of Styrene-Acryl Copolymer Resin-

300 parts by mass of ethyl acetate was placed into a reaction vesselequipped with a cooling tube, an agitator and a nitrogen introducingtube, then, 300 parts by mass of a styrene-acryl monomer mixture(styrene/acrylic acid 2-etherhexyl/acrylic acid/acrylic acid 2-hydroxylethyl=75/15/5/5) and 10 parts by mass of azobisisobutyronitrile were fedthereinto, and a resultant thereof was allowed to react at 60° C. for 15hours under normal pressure in nitrogen atmosphere.

Next, 200 parts by mass of methanol was added to the reaction solutionand agitated for 1 hour. Then, the reaction solution from which asupernatant fluid was removed was dried under reduced pressure, therebyobtaining a styrene-acryl copolymer resin.

-Dissolution of Toner Material or Formulation of Dispersion Solution-

10 parts by mass of the prepolymer, 60 parts by mass of the unmodifiedpolyester, 130 parts by mass of ethyl acetate and 30 parts by mass ofthe styrene-acryl copolymer were placed into a beaker and a resultantwas agitated and dissolved.

Next, 10 parts by mass of microcrystalline wax (isoparaffin content:14.5% by mass, weight-average molecular weight Mw: 650) and 10 parts bymass of the master batch were fed therein. A bead mill (Ultravisco Mill,made by Imex Co., Ltd.) was used to prepare a starting material solutionunder the following conditions: feeding speed, 1 kg/hour;circumferential speed of disk, 6 m/second; loading amount of zirconiabeads with a particle diameter of 0.5 mm, 80% by volume; and passschedule, 3 times. Then, 2.7 parts by mass of the ketimine was addedthereto to dissolve the toner material and prepare the dispersionsolution.

-Formulation of Aqueous Medium Phase-

306 parts by mass of ion exchanged water, 265 parts by mass of 10% bymass of tricalcium phosphate suspension and 0.2 parts by mass of sodiumdodecylbenzene sulfonate were mixed and agitated to uniformly dissolve,thereby preparing an aqueous medium phase.

-Formulation of Emulsion or Dispersion Solution-

150 parts by mass of the aqueous medium phase was placed into a vesseland agitated at 12,000 rpm by using a TK-type homomixer (made by PrimixCorporation). And, 100 parts by mass of a solution or dispersionsolution of the toner material was added thereto, and a resultantthereof was mixed for 10 minutes to prepare an emulsion or dispersionsolution (emulsified slurry).

-Removal of Organic Solvent-

100 parts by mass of the emulsified slurry was placed into a flask atwhich an agitator and a thermometer were set was subjected to a solventremoval process at 30° C. for 12 hours, while being agitated atagitation circumferential speed of 20 m/minute, thereby obtaining adispersed slurry.

-Washing and Drying-

After 100 parts by mass of the dispersed slurry was filtered underreduced pressure, 100 parts by mass of ion exchanged water was added toa filter cake, a resultant thereof was mixed by using a TK-typehomomixer (at 12,000 rpm and for 10 minutes) and, thereafter, filtered.

300 parts by mass of ion exchanged water was added to the thus obtainedfilter cake and a resultant thereof was mixed by using the TK-typehomomixer (at 12,000 rpm and for 10 minutes) and thereafter filtered,the procedure of which was carried out twice.

20 parts by mass of 10% by mass of an aqueous sodium hydroxide solutionwas added to the thus obtained filter cake and a resultant thereof wasmixed by using the TK-type homomixer (at 12,000 rpm and for 30 minutes)and thereafter filtered under reduced pressure.

300 parts by mass of ion exchanged water was added to the thus obtainedfilter cake, and a resultant thereof was mixed by using the TK-typehomomixer (at 12,000 rpm and for 10 minutes) and thereafter filtered.

300 parts by mass of ion exchanged water was added to the thus obtainedfilter cake and a resultant thereof was mixed by using the TK-typehomomixer (at 12,000 rpm and for 10 minutes) and thereafter filtered,the procedure of which was carried out twice.

Further, 20 parts by mass of 10% by mass of hydrochloric acid was addedto the thus obtained filter cake, and a resultant thereof was mixed byusing the TK-type homomixer (at 12,000 rpm and for 10 minutes) andthereafter filtered.

300 parts by mass of ion exchanged water was added to the thus obtainedfilter cake and a resultant thereof was mixed by using the TK-typehomomixer (at 12,000 rpm and for 10 minutes) and thereafter filtered,the procedure of which was repeated twice. Thereby, a final filter cakewas obtained.

The thus obtained final filter cake was dried at 45° C. for 48 hours byusing an air circulation dryer and sieved through a mesh with 75 μmaperture to obtain toner starting particles.

-External Additive Treatment-

0.6 parts by mass of hydrophobic silica with an average particlediameter of 100 nm, 1.0 part by mass of titanium oxide with an averageparticle diameter of 20 nm and 0.8 parts by mass of hydrophobic silicafine particles with an average particle diameter of 15 nm were mixedwith 100 parts by mass of the thus obtained toner starting particles byusing a Henschel mixer to obtain black toner 7.

Yellow toner 7 was prepared in the same manner as in production of theblack toner 7 except that C.I. Pigment Yellow 17 was used in place ofthe carbon black in producing the black toner 7.

Magenta toner 7 was prepared in the same manner as in production of theblack toner 7 except that C.I. Pigment Red 57 was used in place of thecarbon black in producing the black toner 7.

Cyan toner 7 was prepared in the same manner as in production of theblack toner 7 except that C. I. Pigment Blue 15 was used in place of thecarbon black in producing the black toner 7.

The thus obtained black, yellow, magenta and cyan toners 7 were measuredfor an average circularity and a volume average particle diameter Dv inthe following manner, and the average circularity was 0.94 and volumeaverage particle diameter Dv was 5.7 μm.

<Production of Developers 7>

-Production of Carrier-

21.0 parts by mass of an acryl resin solution (toluene solution ofcyclohexylmethacrylate/methylmethacrylate=80/20 (mass ratio) copolymerprepared by synthesis of a monomer made by Mitsubishi Rayon Co., Ltd.,solid content of 50% by mass), 6.4 parts by mass of a guanamine solution(Super Beckamine TD-126, made by DIC Corporation, dry solid content of70% by mass), 7.6 parts by mass of alumina particles (SumicorundomAA-03, made by Sumitomo Chemical Co., Ltd., average particle diameter of0.3 μm, intrinsic resistance value 10¹⁴ (Ω·cm)), 65.0 parts by mass of asilicone resin solution (SR2410, made by Dow Corning Toray Co., Ltd.,dry solid content of 23% by mass), 1.0 part by mass of aminosilane(SH6020, made by Dow Corning Toray Co., Ltd., dry solid content of 100%by mass), 60 parts by mass of toluene and 60 parts by mass of butylcellosolve were dispersed for 10 minutes by using a homomixer, therebyobtaining a coated-film forming solution of alumina particles-containingacryl resin and silicone resin.

Burned ferrite power [(MgO)_(1.8)(MnO)_(49.5)(Fe₂O₃)_(48.0): averageparticle diameter of 35 μm)] was used as a core material, and thecoated-film forming solution was coated on the surface of the corematerial so as to give a thickness of 0.15 μm by using a spira coater(made by Okada Seiko Co., Ltd.) and dried. Thereafter, a producedsubstance was burned by being allowed to stand at 150° C. for 1 hour inan electric furnace. After cooling, the substance was disintegrated byusing a sieve with an aperture of 106 μm to obtain a carrier with aweight average particle diameter of 35 μm.

7 parts by mass of the toners 7 for the respective colors was uniformlymixed with 100 parts by mass of the carrier by using a Turvla mixer inwhich a vessel thereof was moved rotationally to cause agitation, and aresultant thereof was electrically charged, thereby obtaining thedevelopers 7 for the respective colors.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that thedevelopers 1 used in Example 1 were changed to the developer 7. Theresults are shown in Table 2.

Example 11

Evaluation was made in the same manner as in Example 10 except that theimage forming apparatus used in Example 10 (IMAGIO MP C7500, made byRicoh Company Ltd.) was altered and the printing speed in the previouslydescribed <Preparation of printed matter> was decreased by 20% to printprinted matter. The results are shown in Table 2.

Example 12

<Formulation of Overcoat Composition 7>

An overcoat composition 7 was prepared in the same manner as informulation of the overcoat composition 3 except that 80 parts by massof ethylcarbitol acrylate and 2.5 parts by mass of ethoxydiethyleneglycol acrylate used in formulation of the overcoat composition 3 werechanged to 25 parts by mass of ethyl carbitol acrylate, 40 parts by massof ethoxydiethylene glycol acrylate and 15 parts by mass oftrimethylolpropane triacrylate.

The thus obtained overcoat composition 7 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 80mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that theovercoat composition 1 used in Example 1 was changed to the overcoatcomposition 7. The results are shown in Table 2.

Example 13

<Formulation of Overcoat Composition 8>

An overcoat composition 8 was prepared in the same manner as informulation of the overcoat composition 3 except that 80 parts by massof ethyl carbitol acrylate and 2.5 parts by mass of ethoxydiethyleneglycol acrylate used in formulating the overcoat composition 3 werechanged to 50 parts by mass of ethylcarbitol acrylate, 20 parts by massof ethoxydiethylene glycol acrylate and 10 parts by mass oftrimethylolpropane triacrylate.

The thus obtained overcoat composition 8 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 40mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that theovercoat composition 1 used in Example 1 was changed to the overcoatcomposition 8. The results are shown in Table 2.

Comparative Example 1

<Formulation of Overcoat Composition 9>

9 parts by mass of pentaerythritol tetraacrylate as a polymerizableunsaturated compound, 2.5 parts by mass of ethoxydiethylene glycolacrylate as a polymerizable unsaturated compound, 30 parts by mass oftrimethylolpropane triacrylate as a polymerizable unsaturated compoundand 0.3 parts by mass of hydroquinone as a polymerization prohibitingagent were placed into a beaker and heated up to 120° C. whileagitating, and 50 parts by mass of a diallylphthalate prepolymer (DaisoDap 100, made by Daiso Co., Ltd.) was also dissolved therein. Further, 2parts by mass of aluminum isopropylate was dispersed into 2 parts bymass of toluene, which was agitated at 110° C. for 20 minutes whilebeing added gradually. In the meantime, the toluene added as a solventwas removed from a system to obtain a photo-curing varnish base agent.

Next, 75 parts by mass of the photo-curing varnish base agent, 60 partsby mass of 1,9-nonanediol diacrylate as a polymerizable unsaturatedcompound, 10 parts by mass of benzophenone as a photo-polymerizationinitiator, 5 parts by mass of p-dimethylamino acetophenone and 10 partsby mass of phenyl glycol monoacrylate as a viscosity adjusting agentwere mixed and well kneaded by using a three-roll mill, therebyobtaining a photo-curing overcoat composition 9.

The thus obtained overcoat composition 9 was measured for viscosity inthe following manner, which was 200 mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that theovercoat composition 1 used in Example 1 was changed to the overcoatcomposition 9. The results are shown in Table 2.

Comparative Example 2

<Formulation of Overcoat Composition 10>

40 parts by mass of a polyester acrylate oligomer (EBECRYL846,weight-average molecular weight Mw: 1,100, made by Daicel Cytec CompanyLtd.), 2.5 parts by mass of ethoxydiethylene glycol acrylate as apolymerizable unsaturated compound, 30 parts by mass of tripropyleneglycol diacrylate as a polymerizable unsaturated compound, 50 parts bymass of 1,9-nonanediol diacrylate as a polymerizable unsaturatedcompound, 0.2 parts by mass of hydroquinone monomethyl ether as apolymerization prohibiting agent, 8 parts by mass of benzoinethyl etheras a photo-polymerization initiator and 3 parts by mass oftriisopropanol amine as a sensitizing agent were mixed and agitated at60° C. for 20 minutes, thereby obtaining a photo-curing overcoatcomposition 10.

The thus obtained overcoat composition 10 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 470mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 2 except that theovercoat composition 2 used in Example 2 was changed to the overcoatcomposition 10. The results are shown in Table 2.

Comparative Example 3

<Formulation of Overcoat Composition 11>

40 parts by mass of a polyester acrylate oligomer (EBECRYL846,weight-average molecular weight Mw: 1,100, made by Daicel Cytec CompanyLtd.), 2.5 parts by mass of ethoxydiethylene glycol acrylate as apolymerizable unsaturated compound, 30 parts by mass of tripropyleneglycol diacrylate as a polymerizable unsaturated compound, 300 parts bymass of acryloylmorpholine as a polymerizable unsaturated compound, 0.2parts by mass of hydroquinone monomethyl ether as a polymerizationprohibiting agent, 8 parts by mass of benzomethyl ether as aphoto-polymerization initiator and 3 parts by mass of triisopropanolamine as a sensitizing agent were mixed and agitated at 60° C. for 20minutes, thereby obtaining a photo-curing overcoat composition 11.

The thus obtained overcoat composition 11 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 15mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 2 except that theovercoat composition 2 used in Example 2 was changed to the overcoatcomposition 11. The results are shown in Table 2.

Comparative Example 4

<Formulation of Overcoat Composition 12>

60 parts by mass of a polyester acrylate oligomer (EBECRYL1830,weight-average molecular weight Mw: 1,500, made by Daicel Cytec CompanyLtd.), 30 parts by mass of as bisphenol A ethylene oxide adductdiacrylate (V#700, made by Osaka Organic Chemical Industry Ltd.) as apolymerizable unsaturated compound, 5 parts by mass of 2-ethyhexylacrylate as a polymerizable unsaturated compound, 200 parts by mass of1,6-hexanediol diacrylate as a polymerizable unsaturated compound, 2.5parts by mass of ethoxydiethylene glycol acrylate as a polymerizableunsaturated compound, 0.4 parts by mass of 2,6-ditert-butyl-p-cresol(BHT) as a polymerization prohibiting agent and 9 parts by mass ofIrgacure 184 (made by Ciba Specialty Chemicals Inc.) as aphoto-polymerization initiator were mixed and agitated at 60° C. for 20minutes, thereby obtaining a photo-curing overcoat composition 12.

The thus obtained overcoat composition 12 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 200mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 1 except that theovercoat composition 1 used in Example 1 was changed to the overcoatcomposition 12. The results are shown in Table 2.

Comparative Example 5

<Formulation of Overcoat Composition 13>

10 parts by mass of pentaerythritol tetraacrylate, 30 parts by mass oftrimethylol propane acrylate, 0.3 parts by mass of hydroquinone as apolymerization prohibiting agent were placed into a beaker and heated upto 120° C. while agitating, and 50 parts by mass of diallylphthalateprepolymer (Daiso Dap 100, made by Daiso Co., Ltd.) was dissolvedtherein. Further, 2 parts by mass of aluminum isopropylate was dispersedinto 2 parts by mass of toluene, which was agitated at 110° C. for 20minutes, while being added gradually. During this time, the tolueneadded as a solvent was removed from a system, thereby obtaining aphoto-curing varnish base agent.

Next, 75 parts by mass of the photo-curing varnish base agent, 60 partsby mass of 1,9-nonanediol diacrylate, 10 parts by mass of benzophenoneas a photo-polymerization initiator, 5 parts by mass of p-dimethylaminoacetophenone and 10 parts by mass of phenylglycol monoacrylate as aviscosity adjusting agent were mixed and well kneaded by using athree-roll mill, thereby obtaining a photo-curing overcoat composition13.

The thus obtained overcoat composition 13 was measured for viscosity at25° C. in the same manner as in Example 1, and the viscosity was 240mPa·s.

<Evaluation>

Evaluation was made in the same manner as in Example 4 except that theovercoat composition 2 used in Example 4 was changed to the overcoatcomposition 13, and an image forming apparatus (IMAGIO MP C7500, made byRicoh Company Ltd.) was altered to decrease the printing speedpreviously described in <Preparation of printed matter> by 20% to printprinted matter. The results are shown in Table 2.

Comparative Example 6

Evaluation was made in the same manner as in Comparative Example 5except that the image forming apparatus (IMAGIO MP C7500, made by RicohCompany Ltd.) used in Comparative Example 5 was altered to decrease theprinting speed previously described in <<Preparation of printed matter>by 25%, and a single-color toner of a solid image part was given 0.5mg/cm² in adhesion quantity, to print printed matter. The results areshown in Table 2.

TABLE 1-1 Toners (black, magenta, cyan, and yellow) Volume Waxes averageAver- Content particle age (% by diameter circu- No. Type mass) Dv (μm)larity Example 1 1 Microcrystalline wax 5.0 8.0 0.90 Example 2 2Microcrystalline wax + 5.0 6.8 0.91 Paraffin wax Example 3 3Microcrystalline wax + 5.0 7.9 0.91 Paraffin wax Example 4 4 Paraffinwax 5.0 8.0 0.89 Example 5 5 Paraffin wax 1.6 7.8 0.90 Example 6 6Microcrystalline wax + 5.0 7.8 0.91 Paraffin wax Example 7 1Microcrystalline wax 5.0 8.0 0.90 Example 8 1 Microcrystalline wax 5.08.0 0.90 Example 9 1 Microcrystalline wax 5.0 8.0 0.90 Example 10 7Microcrystalline wax 8.3 5.7 0.94 Example 11 7 Microcrystalline wax 8.35.7 0.94 Example 12 1 Microcrystalline wax 5.0 8.0 0,90 Example 13 1Microcrystalline wax 5.0 8.0 0.90 Comparative 1 Microcrystalline wax 5.08.0 0.90 Example 1 Comparative 2 Microcrystalline wax + 5.0 6.8 0.91Example 2 Paraffin wax Comparative 2 Microcrystalline wax + 5.0 6.8 0.91Example 3 Paraffin wax Comparative 1 Microcrystalline wax 5.0 8.0 0.90Example 4 Comparative 4 Paraffin wax 5.0 8.0 0.89 Example 5 Comparative4 Paraffin wax 5.0 8.0 0.89 Example 6

TABLE 1-2 Overcoat composition Polymerizable unsaturated compoundContent Viscosity of A + B + C No. (mPa · s) Surfactant Type (% by mass)Example 1 1 200 Not used A D E K — 37.5 Example 2 2 460 Not used B F K —— 37.4 Example 3 2 460 Not used B F K — — 37.4 Example 4 2 460 Not usedB F K — — 37.4 Example 5 2 460 Not used B F K — — 37.4 Example 6 3 20Not used A G C K — 80.8 Example 7 4 740 Not used A H I K — 15.8 Example8 5 180 Used A D E K — 37.6 Example 9 6 410 Used A H I K — 15.8 Example10 1 200 Not used A D E K — 37.5 Example 11 1 200 Not used A D E K —37.5 Example 12 7 80 Not used A G C K E 44.8 Example 13 8 40 Not used AG C K E 61.8 Comparative 9 200 Not used J D E K — 0 Example 1Comparative 10 470 Not used J F K — — 0 Example 2 Comparative 11 15 Notused B F K — — 78.2 Example 3 Comparative 12 200 Not used A H I K — 65.2Example 4 Comparative 13 240 Not used D E J — — 0 Example 5 Comparative13 240 Not used D E J — — 0 Example 6 Polymerizable unsaturatedcompounds A: 1,6-hexanediol diacrylate B: acryloylmorpholine C:ethylcarbitol acrylate D: pentaerythritol tetraacrylate E:trimethylolpropane triacrylate F: tripropylene glycol diacrylate G:cyclohexyl acrylate H: bisphenol A ethylene oxide adduct diacrylate I:2-ethylhexyl acrylate J: 1,9-nonanediol diacrylate K: ethoxydiethyleneglycol acrylate

TABLE 2-1 Solid fixed Overcoat image Fusion property Developercomposition Wax coverage Color No. No. factor (%) difference ΔE* Example1 1 1 44 5.8 Example 2 2 2 60 4.6 Example 3 3 2 63 4.6 Example 4 4 2 664.6 Example 5 5 2 33 4.6 Example 6 6 3 41 27.8 Example 7 1 4 44 3.5Example 8 1 5 44 6.2 Example 9 1 6 44 5.0 Example 10 7 1 52 5.3 Example11 7 1 58 5.3 Example 12 1 7 44 9.8 Example 13 1 8 44 18.9 Comparative 19 66 2.0 Example 1 Comparative 2 10 66 0.5 Example 2 Comparative 2 11 6633.0 Example 3 Comparative 1 12 66 31.0 Example 4 Comparative 4 13 692.5 Example 5 Comparative 4 13 73 2.5 Example 6

TABLE 2-2 Evaluation Repelling property Attachment State of(wettability) property image Example 1 A A A Example 2 A A A Example 3 AA A Example 4 B B A Example 5 A A A Example 6 A A B Example 7 A B AExample 8 A A A Example 9 A B A Example 10 A A A Example 11 A A AExample 12 A A A Example 13 A B A Comparative B D B Example 1Comparative B D B Example 2 Comparative B A C Example 3 Comparative B AC Example 4 Comparative C D A Example 5 Comparative D D A Example 6

Aspects of the present invention are, for example, as follows.

<1> A color image forming method, including:

forming an electrostatic latent image on an electrostatic latent imagebearing member;

developing the electrostatic latent image to form a visible image withat least two toners each containing a releasing agent and being selectedfrom black toner, magenta toner, cyan toner and yellow toner;

transferring the visible image to a recording medium;

fixing the transferred image on the recording medium with a fixingmember having no releasing agent on a surface thereof; and

forming an overcoat layer on the fixed image, the overcoat layer beingformed by polymerizing an overcoat composition,

wherein when lightness L1, chromaticity a1 and chromaticity b1 accordingto an L*a*b* color system of the fixed image formed with the at leasttwo toners as well as lightness L2, chromaticity a2 and chromaticity b2according to the L*a*b* color system of the fixed image obtained afterthe overcoat composition is dropped at 0.4 mg/cm² from a height of 10 mmabove the fixed image and the overcoat composition is removed after 10seconds have passed are applied to the following formula (1), a colordifference ΔE* is from 3.0 to 30.0:ΔE*[(a2−a1)²+(b2−b1)²+(L2−L1)²]^(1/2)  (1).

<2> The color image forming method according to <1>, wherein the colordifference ΔE* is from 4.0 to 20.0.

<3> The color image forming method according to <2>, wherein the colordifference ΔE* is from 4.0 to 10.0.

<4> The color image forming method according to <1> or <2>, wherein whenat least any one of red, green and blue fixed solid images formed withthe at least two toners using a test chart No. 4 according to ISO/IEC15775:1999 is exposed to saturated vapor of an aqueous rutheniumtetroxide solution and is then radiated with electron beams ataccelerating voltage of 0.8 kV to thereby obtain a reflection electronimage and the reflection electron image is converted to a binarizationimage formed of a black part and a white part, an area percentage of theblack part with respect to an entire area of the binarization image isfrom 40% to 70%.

<5> The color image forming method according to <4>, wherein the areapercentage of the black part with respect to an entire area of thebinarization image is from 42% to 65%.

<6> The color image forming method according to any one of <1> to <5>,wherein the overcoat composition contains at least one polymerizableunsaturated compound selected from 1,6-hexanediol diacrylate, ethylcarbitol acrylate and acryloylmorpholine, and the content of thepolymerizable unsaturated compound is from 20% by mass to 60% by mass.

<7> The color image forming method according to any one of <1> to <6>,wherein the overcoat composition contains a surfactant.

<8> The color image forming method according to any one of <1> to <7>,wherein a viscosity of the overcoat composition is 30 mPa·s to 700 mPa·sat 25° C.

<9> The color image forming method according to any one of <1> to <8>,wherein the releasing agent contains microcrystalline wax.

<10> A color image forming apparatus, including:

an electrostatic latent image bearing member;

an electrostatic latent image forming unit which forms an electrostaticlatent image on the electrostatic latent image bearing member;

a development unit which develops the electrostatic latent image to forma visible image with at least two toners each containing a releasingagent and being selected from black toner, magenta toner, cyan toner andyellow toner;

a transfer unit which transfers the visible image to a recording medium;

a fixing unit which fixes the transferred image on the recording mediumwith a fixing member having no releasing agent on a surface thereof, and

an overcoat layer forming unit which forms an overcoat layer on thefixed image by polymerizing an overcoat composition,

wherein when lightness L1, chromaticity a1 and chromaticity b1 accordingto an L*a*b* color system of the fixed image formed with the at leasttwo toners as well as lightness L2, chromaticity a2 and chromaticity b2according to the L*a*b* color system of the fixed image obtained afterthe overcoat composition is dropped at 0.4 mg/cm² from a height of 10 mmabove the fixed image and the overcoat composition is removed after 10seconds have passed are applied to the following formula (1), a colordifference ΔE* is from 3.0 to 30.0:ΔE*=[(a2−a1)²+(b2−b1)²+(L2−L1)²]^(1/2)  (1).

<11> The color image forming apparatus according to <10>, wherein thecolor difference ΔE* is from 4.0 to 20.0.

<12> The color image forming apparatus according to <11>, wherein thecolor difference ΔE* is from 4.0 to 10.0.

<13> The color image forming apparatus according to <8>, wherein when atleast any one of red, green and blue fixed solid images formed with theat least two toners using a test chart No. 4 according to ISO/IEC15775:1999 is exposed to saturated vapor of an aqueous rutheniumtetroxide solution and is then radiated with electron beams ataccelerating voltage of 0.8 kV to obtain a reflection electron image andthe reflection electron image is converted to a binarization imageformed of a black part and a white part, an area percentage of the blackpart with respect to an entire area of the binarization image is from40% to 70%.

<14> The color image forming apparatus according to <13>, wherein thearea percentage of the black part with respect to an entire area of thebinarization image is from 42% to 65%.

This application claims priority to Japanese application No.2012-161735, filed on Jul. 20, 2012, and incorporated herein byreference.

What is claimed is:
 1. A color image forming method, comprising: formingan electrostatic latent image on an electrostatic latent image bearingmember; developing the electrostatic latent image to form a visibleimage with at least two toners each containing a releasing agent andbeing selected from black toner, magenta toner, cyan toner and yellowtoner; transferring the visible image to a recording medium; fixing thetransferred image on the recording medium with a fixing member having noreleasing agent on a surface thereof; and forming an overcoat layer onthe fixed image, the overcoat layer being formed by polymerizing anovercoat composition, wherein when lightness L1, chromaticity a1 andchromaticity b1 according to an L*a*b* color system of the fixed imageformed with the at least two toners as well as lightness L2,chromaticity a2 and chromaticity b2 according to the L*a*b* color systemof the fixed image obtained after the overcoat composition is dropped at0.4 mg/cm² from a height of 10 mm above the fixed image and the overcoatcomposition is removed after 10 seconds have passed are applied to thefollowing formula (1), a color difference ΔE* is from 3.0 to 30.0:ΔE*=[(a2−a1)²+(b2−b1)²+(L2−L1)²]^(1/2)  (1), and wherein when at leastany one of red, green and blue fixed solid images formed with the atleast two toners using a test chart No. 4 according to ISO/IEC15775:1999 is exposed to saturated vapor of an aqueous rutheniumtetroxide solution and is then radiated with electron beams ataccelerating voltage of 0.8 kV to thereby obtain a reflection electronimage and the reflection electron image is converted to a binarizationimage formed of a black part and a white part, an area percentage of theblack part with respect to an entire area of the binarization image isfrom 40% to 70%.
 2. The color image forming method according to claim 1,wherein the color difference ΔE* is from 4.0 to 20.0.
 3. The color imageforming method according to claim 1, wherein the color difference ΔE* isfrom 4.0 to 10.0.
 4. The color image forming method according to claim1, wherein the area percentage of the black part with respect to anentire area of the binarization image is from 42% to 65%.
 5. The colorimage forming method according to claim 1, wherein the overcoatcomposition contains at least one polymerizable unsaturated compoundselected from 1,6-hexanediol diacrylate, ethyl carbitol acrylate andacryloylmorpholine, and the content of the polymerizable unsaturatedcompound is from 20% by mass to 60% by mass.
 6. The color image formingmethod according to claim 1, wherein the overcoat composition contains asurfactant.
 7. The color image forming method according to claim 1,wherein a viscosity of the overcoat composition is 30 mPa·s to 700 mPa·s at 25° C.
 8. The color image forming method according to claim 1,wherein the releasing agent contains microcrystalline wax.